Numdiff User Manual
1 Copying
2 Acknowledgments
3 Overview
  3.1 Output format
  3.2 Overview mode
  3.3 Output of the filter
  3.4 Raw output
4 Installing
5 Invoking numdiff
6 Selecting lines and fields for the comparison
7 Invoking ndselect
8 Using the filter of numdiff
9 Warnings
Appendix A GNU Free Documentation License
Index
Numdiff User Manual
*******************

_"...und der eignen Kraft vertrauend steigt ein frei Geschlecht empor!"_


This manual describes how to install and use Numdiff, a program which
compares putatively similar files line by line and field by field,
ignoring small numeric differences or/and different numeric formats.

   Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013,
2014, 2015, 2016, 2017 Ivano Primi <ivprimi(at)libero(dot)it>

     Permission is granted to copy, distribute and/or modify this
     document under the terms of the GNU Free Documentation License,
     Version 1.3 or any later version published by the Free Software
     Foundation; with no Invariant Sections, no Front-Cover Texts, and
     no Back-Cover Texts.  A copy of the license is included in *note
     GNU Free Documentation License::.

1 Copying
*********

Numdiff (also written numdiff) is free software: you can redistribute it
and/or modify it under the terms of the GNU General Public License as
published by the Free Software Foundation, either version 3 of the
License, or (at your option) any later version.

   Numdiff is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
Public License for more details.

   You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.

2 Acknowledgments
*****************

I want to thank Mr.  Norman Clerman <norm(dot)opcon(at)fuse(dot)net> for
several suggestions he gave me to improve the readability and the
effectiveness of the output produced by Numdiff.  He also pointed out
the need to implement a filter to resynchronize the lines between two
files in case of addition or deletion of one or more lines.  I have to
give him credit for the urge to prepare the versions 4.x and 5.x of
Numdiff.

   Moreover, I want to thank my friends Mariapia Palombaro, since she
removed some errors while reviewing the first version of this document,
and Paolo Caramanica, who suggested me to add more information to the
output of the option '-S'.

3 Overview
**********

Computer users often find occasion to ask how two files differ.  Perhaps
one file is a newer version of the other file.  Or maybe the two files
started out as identical copies but were changed by different people.

   There are several ways to look at the differences between two files.
One way consists in looking at the series of lines that were deleted
from, inserted in, or changed in one file to produce the other file.
The well-known 'diff' program compares two files line by line, finds
groups of lines that differ, and reports each group of differing lines.
Without particular options, when comparing lines the 'diff' program
considers any change in the amount or in the type of the characters as a
difference.  However, trough some command line options the user can
suppress the output of certain kinds of differences that are not
important to him.  For instance, 'diff' provides options to ignore
differences in the amount of white space between words or lines, or
differences in alphabetic case.

   Another way to look at the differences between two files consists in
considering the words that were deleted from, inserted in, or changed in
one file to produce the other file.  Here "word" refers to a sequence of
non white-space characters delimited by a couple of white-spaces, one
before and the other one after the word.

   The 'wdiff' program by Franc,ois Pinard
<pinard(at)iro(dot)umontreal(dot)ca> compares words in two files and
reports the differences.

   Finally, one can regard the differences between two files as a
sequence of pairs of differing bytes.  The 'cmp' program reports the
differences between two files byte by byte, instead of line by line or
word by word.  As a result, it is often more useful than 'diff' or
'wdiff' for comparing binary files.

   However, none of these approaches turns out to be good when you want
to compare a couple of text files composed partially or entirely by
numerical fields.  In such a case what you want to obtain usually is a
list of the numerical fields in the second file which *numerically*
differ from the corresponding fields in the first file.  But, while a
number can be written using different notations, programs like 'diff' or
'wdiff' can not recognize whether a difference between two numeric
fields is only due to the notation or is actually a difference of
numerical values.

   For instance, 11.23 and 11.2300000 are the same number but
represented in different ways.  If you are interested in the numerical
values, the difference in the representation is not meaningful and then
should be ignored.  However, 'diff' and 'wdiff' always consider the
previous one as an actual difference: there is no way for you to tell
these programs to ignore it.

   Another example of this type is given by 98765.4321 and
9.87654321E04.  Here the difference is only due to the use of the
scientific notation in place of the ordinary decimal notation.

   In addition, depending on your country you could stick to different
conventions in writing numbers.  For example, the amount "three hundred
millions and fifty-two thousands of dollars and forty-six cents" is
usually written by an Italian accountant as 300.052.000,46$ while an
American accountant would write 300,052,000.46$.  Of course,
300.052.000,46$ and 300,052,000.46$ represent the same amount of money
but 'diff' and 'wdiff' would report a difference, which probably is not
what you want in such a case.

   Lastly, sometimes you could wish to ignore even differences in
numerical values as long as they do not exceed a certain threshold.  In
other words, you could desire to suppress the report of all "small"
numerical differences.

   For example, it could happen that you want to ignore all numerical
differences whose absolute value is not greater than 0.0001.  If this is
the case, then the numerical fields 33 and 33.00009 should be considered
equal, while 33 and 33.00011 should be reported as different.

   However, 'diff' and 'wdiff' can not be used to ignore small numerical
differences, since they do not even know what a numerical difference is.

   These are the reasons why I decided to implement a new program with
the capability to appropriately compare files containing numerical
fields.  In writing this program I was inspired by 'ndiff', a GPL'ed
software by Nelson H. Baabe of the Salt Lake City University.  'ndiff'
is actually a good tool, and I used it for a while.  But I did not
completely like the way it works, and so 'numdiff' was conceived.
Although 'ndiff' inspired 'numdiff', they are completely different from
the viewpoint of the source code: 'numdiff' has been entirely written
from scratch with the addition of code coming from GNU bc, GNU diff and
GNUlib.  In addition, the last versions of Numdiff offer much more
features than 'ndiff' does.

   'numdiff' can be used to compare putatively similar files line by
line and field by field, ignoring small numeric differences or/and
different numeric formats.  'numdiff' takes two mandatory arguments, the
paths of the two files to compare, and, after splitting them into lines
and the lines into fields according to a given list of field delimiters,
it compares every field of every line of the first file with the
corresponding field of the second file.  What _corresponding_ here
exactly means depends on the options passed to the program on the
command line.  With no options, corresponding means the field of the
second file at the same position, where position refers both to the line
number and to the location within the line.  If the compared fields are
both legal numerical values, then 'numdiff' performs a numerical
comparison between them, otherwise it performs a literal comparison,
i.e.  the usual byte-by-byte comparison.  In case of literal comparison,
two fields are regarded as equal if they are formed by the same sequence
of characters.  In case of numerical comparison and without specific
command line options, two fields are regarded as equal if their
numerical difference is zero.  Mind that, if you do not explicitly
specify a list of field delimiters by means of the option '-s' or '-D',
'numdiff' takes as field delimiters the characters newline ('\n', ASCII
code 0x0A), horizontal tabulation ('\t', ASCII code 0x09), and blank ('
', ASCII code 0x20).

   For example, if the file 'list1' contains the data
accident        123     23Joshua          34.55           +3+4i	        water
dog       -3455.321     cat             2.345678e-9     .0005-6.23e2i


and file 'list2' contains the data

Accident        123     23456          34.5500         +3.0001+4i
dog       -3455.320098  Cat     +2.345678e-9            -6.23e2i    $$$
A new line


then the output of the command 'numdiff list1 list2' will be:

     ----------------
     ##1       #:1   <== accident
     ##1       #:1   ==> Accident
     @                                                     @@
     ##1       #:3   <== 23Joshua
     ##1       #:3   ==> 23456
     @                                                     @@
     ##1       #:5   <== +3+4i
     ##1       #:5   ==> +3.0001+4i
     @ Absolute error = 1.0000000000e-4, Relative error = 2.0000000000e-5
     ##1       #>6   <== water
     ##1             ==>
     @ Line 1 in file "list2" is shorter than expected!
     ----------------
     ##2       #:2   <== -3455.321
     ##2       #:2   ==> -3455.320098
     @ Absolute error = 9.0200000000e-4, Relative error = 2.6104672633e-7
     ##2       #:3   <== cat
     ##2       #:3   ==> Cat
     @                                                     @@
     ##2       #:5   <== .0005-6.23e2i
     ##2       #:5   ==> -6.23e2i
     @ Absolute error = 5.0000000000e-4, Relative error = 8.0256821830e-7
     ##2             <==
     ##2       #>6   ==> $$$
     @ Line 2 in file "list1" is shorter than expected!
     ----------------
     ##3             <==
     ##3       #>1   ==> A new line
     @ Line 3 in file "list1" is shorter than expected!
     ----------------
               <==
     ##4       ==>


     +++  File "list1" differs from file "list2"

   At the same time 'numdiff' will print the following error message on
stderr:
     ***  End of file "list1" reached while trying to read line 4.
          File "list2" has more lines than file "list1",
          line 4 is the last one read from file "list2"

   It is worth remarking that 'numdiff' can recognize complex numbers,
provided that they are written in the form a+bi or a-bi with no extra
characters between the values a, b and the sign + or - (the symbol i,
used to represent the imaginary unit, can be changed by a suitable
command line option, *note Invoking numdiff::).  Do not worry if you do
not know what complex numbers are: probably you will never manage files
containing complex numbers, thus you can live happily without them.  :)

   We consider now an example which shows how Numdiff can resynchronize
the lines between two files in case of addition or deletion of one or
more lines.  The versions of Numdiff prior to 5 did not work well if one
of the two files to compare contains in the middle some lines more or
less than the other one.  For instance, if you have one file that is
1000 lines long that you are comparing to a second file 1001 lines long,
and except for that one extra line, located, let us say, at line 500,
the files are identical, then 'numdiff' version 4.x does *not* show only
the one line difference: once the files are out of synchronization
'numdiff' 4.x reports every line as different.  Since version 5 it is
possible in such cases to activate a filter which handles additions and
deletions of lines.  There are several options ruling how the filter
actually works, and I will give later a detailed explanation on how to
use them to obtain each time the wished result.  The simplest way to
activate the filter consists in using the option '-z @'.  If 'bill1' and
'bill2' are given by
 Month          Expenses
-------------------------
 Jan09          $  233.56
 Feb09          $  850.77
 Mar09          $   12.55
 Apr09          $  524.00
 May09          $   78.25
 Jun09          $  230.00
 Jul09          $  443.10
 Aug09          $   67.65
 Sep09          $   10.00
 Oct09          $  201.45
 Nov09          $  110.00
 Dec09          $  200.27
-------------------------
Total           $ 2961.60

and

 Month          Expenses
 Jan09          $  234.00
 Mar09          $   13.00
 May09          $   78.25
 Jul09          $  443.10
 Sep09          $   10.00
 Nov09          $  110.00
 Jan10          $  200.00
-------------------------

Total           $ 1088.35

respectively, then the differences between the two files are:
   * the insertion of the separator ------------------------- in 'bill1'
     before the list of the months,
   * the deletion in 'bill2' of the lines related to the expenses for
     the months February, April, June, August, October, December,
   * small changes in 'bill2' to the expenses of the months January 2009
     and March,
   * the presence in 'bill2' of an entry for January 2010 just before
     the separator -------------------------,
   * the addition of an empty line to 'bill2' after the separator
     -------------------------,
   * and the different values for the total sum of the expenses.

   The output of the command 'numdiff -z @ -V bill1 bill2' (I have added
here the option '-V' to let Numdiff show which couples of lines it is
comparing each time) shows exactly the expected differences:

     ----------------
     ##2       <== -------------------------
               ==>

     ----------------
     ##3       <==  Jan09          $  233.56
     ##2       ==>  Jan09          $  234.00

     ##3       #:3   <== 233.56
     ##2       #:3   ==> 234.00
     @ Absolute error = 4.4000000000e-1, Relative error = 1.8838842268e-3
     ----------------
     ##4       <==  Feb09          $  850.77
               ==>

     ----------------
     ##5       <==  Mar09          $   12.55
     ##3       ==>  Mar09          $   13.00

     ##5       #:3   <== 12.55
     ##3       #:3   ==> 13.00
     @ Absolute error = 4.5000000000e-1, Relative error = 3.5856573705e-2
     ----------------
     ##6       <==  Apr09          $  524.00
               ==>

     ----------------
     ##8       <==  Jun09          $  230.00
               ==>

     ----------------
     ##10      <==  Aug09          $   67.65
               ==>

     ----------------
     ##12      <==  Oct09          $  201.45
               ==>

     ----------------
     ##14      <==  Dec09          $  200.27
     ##8       ==>  Jan10          $  200.00

     ##14      #:1   <== Dec09
     ##8       #:1   ==> Jan10
     @                                                     @@
     ##14      #:3   <== 200.27
     ##8       #:3   ==> 200.00
     @ Absolute error = 2.7000000000e-1, Relative error = 1.3500000000e-3
     ----------------
               <==
     ##10      ==>

     ----------------
     ##16      <== Total           $ 2961.60
     ##11      ==> Total           $ 1088.35

     ##16      #:3   <== 2961.60
     ##11      #:3   ==> 1088.35
     @ Absolute error = 1.8732500000e+3, Relative error = 1.7211834428e+0

     +++  File "bill1" differs from file "bill2"

   Looking at the displayed report we see that:
   * the second line of file 'bill1', i.e.  the one containing the
     separator, has no correspondance, or, if you prefer, has been
     deleted from file 'bill2'.
   * The lines related to the months January and March 2009 have been
     slightly modified in 'bill2', namely the values of the expenses are
     slightly different.  Notice that the line with the expenses for
     January 2009 is the third one in file 'bill1' and the second one in
     file 'bill2'.  This information is printed by Numdiff in the form
          ##3       <==  Jan09          $  233.56
          ##2       ==>  Jan09          $  234.00
     Analogously,
          ##5       <==  Mar09          $   12.55
          ##3       ==>  Mar09          $   13.00
     says that the line for March is the fifth one in 'bill1' and the
     third one in 'bill2'.
   * The line related to the total amount of the expenses appears also
     differently in the two files, since the amount of the expenses is
     different.  Notice that this line is the 16th one in file 'bill1'
     and the 11th one in file 'bill2'.
   * The lines related to the months February, April, June, August and
     October, i.e.  the lines no.  4, 6, 8, 10, and 12 of 'bill1', are
     not present in 'bill2'.
   * The line of 'bill1' with the expenses for December 2009 is replaced
     in 'bill2' by the line containing the value of the expenses for
     January 2010.
   * The tenth line of 'bill2', i.e.  the empty line after the
     separator, is not present in 'bill1'.  With respect to 'bill1' this
     line represents then an addition.

   If you compare 'bill1' and 'bill2' without using the option '-z @',
the result is completely misleading.  This is the output of 'numdiff -V
bill1 bill2':

     ----------------
     ##2       <== -------------------------
     ##2       ==>  Jan09          $  234.00

     ##2       #:1   <== -------------------------
     ##2       #:1   ==> Jan09
     @                                                     @@
     ##2             <==
     ##2       #>2   ==> $  234.00
     @ Line 2 in file "bill1" is shorter than expected!
     ----------------
     ##3       <==  Jan09          $  233.56
     ##3       ==>  Mar09          $   13.00

     ##3       #:1   <== Jan09
     ##3       #:1   ==> Mar09
     @                                                     @@
     ##3       #:3   <== 233.56
     ##3       #:3   ==> 13.00
     @ Absolute error = 2.2056000000e+2, Relative error = 1.6966153846e+1
     ----------------
     ##4       <==  Feb09          $  850.77
     ##4       ==>  May09          $   78.25

     ##4       #:1   <== Feb09
     ##4       #:1   ==> May09
     @                                                     @@
     ##4       #:3   <== 850.77
     ##4       #:3   ==> 78.25
     @ Absolute error = 7.7252000000e+2, Relative error = 9.8724600639e+0
     ----------------
     ##5       <==  Mar09          $   12.55
     ##5       ==>  Jul09          $  443.10

     ##5       #:1   <== Mar09
     ##5       #:1   ==> Jul09
     @                                                     @@
     ##5       #:3   <== 12.55
     ##5       #:3   ==> 443.10
     @ Absolute error = 4.3055000000e+2, Relative error = 3.4306772908e+1
     ----------------
     ##6       <==  Apr09          $  524.00
     ##6       ==>  Sep09          $   10.00

     ##6       #:1   <== Apr09
     ##6       #:1   ==> Sep09
     @                                                     @@
     ##6       #:3   <== 524.00
     ##6       #:3   ==> 10.00
     @ Absolute error = 5.1400000000e+2, Relative error = 5.1400000000e+1
     ----------------
     ##7       <==  May09          $   78.25
     ##7       ==>  Nov09          $  110.00

     ##7       #:1   <== May09
     ##7       #:1   ==> Nov09
     @                                                     @@
     ##7       #:3   <== 78.25
     ##7       #:3   ==> 110.00
     @ Absolute error = 3.1750000000e+1, Relative error = 4.0575079872e-1
     ----------------
     ##8       <==  Jun09          $  230.00
     ##8       ==>  Jan10          $  200.00

     ##8       #:1   <== Jun09
     ##8       #:1   ==> Jan10
     @                                                     @@
     ##8       #:3   <== 230.00
     ##8       #:3   ==> 200.00
     @ Absolute error = 3.0000000000e+1, Relative error = 1.5000000000e-1
     ----------------
     ##9       <==  Jul09          $  443.10
     ##9       ==> -------------------------

     ##9       #:1   <== Jul09
     ##9       #:1   ==> -------------------------
     @                                                     @@
     ##9       #>2   <== $  443.10
     ##9             ==>
     @ Line 9 in file "bill2" is shorter than expected!
     ----------------
     ##10      <==  Aug09          $   67.65
     ##10      ==>

     ##10      #>1   <== Aug09          $   67.65
     ##10            ==>
     @ Line 10 in file "bill2" is shorter than expected!
     ----------------
     ##11      <==  Sep09          $   10.00
     ##11      ==> Total           $ 1088.35

     ##11      #:1   <== Sep09
     ##11      #:1   ==> Total
     @                                                     @@
     ##11      #:3   <== 10.00
     ##11      #:3   ==> 1088.35
     @ Absolute error = 1.0783500000e+3, Relative error = 1.0783500000e+2
     ----------------
     ##12      <==  Oct09          $  201.45
               ==>


     ***  End of file "bill2" reached while trying to read line 12.
          File "bill1" has more lines than file "bill2",
          line 12 is the last one read from file "bill1"


     +++  File "bill1" differs from file "bill2"
   Numdiff compares now the first, second, third line of 'bill1' with
the first, second, third line of 'bill2', and so on.  But probably this
is not what you want in such a case: what is reasonable here is to
compare entries related to the same month and not lines having the same
location, i.e.  the same line number.

   Numdiff offers also an option to run just the filter and see how it
resynchronizes the two given files without performing any comparison of
corresponding lines.  The output of 'numdiff -z @ -f bill1 bill2' is
      Month          Expenses          Month          Expenses
     -------------------------     <
      Jan09          $  233.56         Jan09          $  234.00
      Feb09          $  850.77     <
      Mar09          $   12.55         Mar09          $   13.00
      Apr09          $  524.00     <
      May09          $   78.25         May09          $   78.25
      Jun09          $  230.00     <
      Jul09          $  443.10         Jul09          $  443.10
      Aug09          $   67.65     <
      Sep09          $   10.00         Sep09          $   10.00
      Oct09          $  201.45     <
      Nov09          $  110.00         Nov09          $  110.00
      Dec09          $  200.27     |   Jan10          $  200.00
     -------------------------        -------------------------
                                   >
     Total           $ 2961.60        Total           $ 1088.35


     +++  File "bill1" differs from file "bill2"

and shows that the filter is doing its job in the right way, associating
the lines according to the month and not to the line number.  Running
just the filter is extremely useful in all situations when you are not
sure if the filter is working as you wish.  You have indeed to instruct
the filter in the right way to let it work correctly, and this requires
the use of different options depending on the structure of the files to
compare.  Since guessing the right options can be sometimes tricky,
running just the filter and see the result is the best way to be certain
that you are setting up everything correctly.  Later, *note Filtering::,
I will explain in detail
   * what the filter does behind the scenes to understand if and how it
     has to resynchronize the files to compare,
   * and how the related options affect the action of the filter.

   By the way, it is even possible to use '-f' without any other
additional option for the filter, like in 'numdiff -f bill1 bill2', but
the result is more or less the same you would obtain by performing a
byte-by-byte comparison with removal of the field delimiters.

   The option '-f' can be followed by an argument in the form of an
integer number whose meaning will be explained later, *note Use of the
option -f::.

   Even if the output of 'numdiff' is supposed to be self-explanatory,
in the next section I will explain in details all you should know about
it.

3.1 Output format
=================

Let us go back to our first example.  If the files 'list1' and 'list2'
contain the data
accident        123     23Joshua          34.55           +3+4i	        water
dog       -3455.321     cat             2.345678e-9     .0005-6.23e2i


and

Accident        123     23456          34.5500         +3.0001+4i
dog       -3455.320098  Cat     +2.345678e-9            -6.23e2i    $$$
A new line


respectively, then the output of the command 'numdiff list1 list2' will
be:

     ----------------
     ##1       #:1   <== accident
     ##1       #:1   ==> Accident
     @                                                     @@
     ##1       #:3   <== 23Joshua
     ##1       #:3   ==> 23456
     @                                                     @@
     ##1       #:5   <== +3+4i
     ##1       #:5   ==> +3.0001+4i
     @ Absolute error = 1.0000000000e-4, Relative error = 2.0000000000e-5
     ##1       #>6   <== water
     ##1             ==>
     @ Line 1 in file "list2" is shorter than expected!
     ----------------
     ##2       #:2   <== -3455.321
     ##2       #:2   ==> -3455.320098
     @ Absolute error = 9.0200000000e-4, Relative error = 2.6104672633e-7
     ##2       #:3   <== cat
     ##2       #:3   ==> Cat
     @                                                     @@
     ##2       #:5   <== .0005-6.23e2i
     ##2       #:5   ==> -6.23e2i
     @ Absolute error = 5.0000000000e-4, Relative error = 8.0256821830e-7
     ##2             <==
     ##2       #>6   ==> $$$
     @ Line 2 in file "list1" is shorter than expected!
     ----------------
     ##3             <==
     ##3       #>1   ==> A new line
     @ Line 3 in file "list1" is shorter than expected!
     ----------------
               <==
     ##4       ==>


     +++  File "list1" differs from file "list2"

   'numdiff' prints a report on the standard output for every field of
the first file which differs from the corresponding field of the second
file.

   This report indicates first the locations of the fields, namely the
numbers of the lines where the fields appear and their positions within
the line.  The position in the line is "1" for the first field of a
line, "2" for the second field, "3" for the third one, and so on: fields
are numerated starting from the left hand of the line and proceeding
towards the right hand.  For each report the line number is introduced
by the symbol "##", while the field number by "#:".  Then 'numdiff'
shows in what the difference consists.  For example,
     ##1       #:1   <== accident
     ##1       #:1   ==> Accident
     @                                                     @@

means that the first field of the first line is "accident" in the first
file, while in the second file it appears as "Accident".  This
difference could be then canceled by removing "accident" from the first
file and inserting "Accident" in place of it.  The arrows "<==" and
"==>" try to visualize this idea.  Analogously,
     ##2       #:2   <== -3455.321
     ##2       #:2   ==> -3455.320098
     @ Absolute error = 9.0200000000e-4, Relative error = 2.6104672633e-7

means that the second field of the second line is "-3455.321" in the
first file and "-3455.320098" in the second one.  Since the contents of
the field are numerical in both files, 'numdiff' also prints the
absolute and relative errors.

   The absolute error (or absolute difference) is given by the absolute
value of the difference between the values appearing in the two files.

   The relative error (or relative difference) is actually defined in a
more complicated way.  If _n1_ is the value appearing in the first file
and _n2_ is the value in the second file, then the absolute error is
given by the formula _A=|n1-n2|_, while the relative error _R_ is given
by:

   * _R = 0_ if _n1_ and _n2_ are equal,
   * _Inf_ (infinity) if _n2_ differs from _n1_ and at least one of them
     is zero,
   * _R = A/ min(|n1|, |n2|)_ if _n1_ and _n2_ are both non zero and
     _n2_ differs from _n1_.  _min(|n1|, |n2|)_ denotes the minimum
     between the absolute value of _n1_ and the absolute value of _n2_.

With these definitions of absolute and relative error it turns out that
_A(n2, n1) = A(n1, n2)_ and _R(n2, n1) = R(n1, n2)_.  In other words,
the absolute/relative error does not change if you only change the order
of the compared values.  Since version 5 it is actually possible to let
Numdiff compute the relative error always with respect to the value from
the first file or always with respect to the value from the second file,
instead of using the preceding formula.  This can be done through the
option '-F', *note Alternative formulas for the computation of the
relative difference::.

   If at least one of the compared fields is not numerical, then the
output line reporting absolute and relative errors is replaced by the
separator:
@                                                     @@

   It can happen that a line in one of the two files to compare contains
more fields than the corresponding line of the other file.  If this is
the case, 'numdiff' reports this difference by telling that a certain
line (identified by its line number) appears to be shorter than
expected, just as in
     ##1       #>6   <== water
     ##1             ==>
     @ Line 1 in file "list2" is shorter than expected!

   or in
     ##3             <==
     ##3       #>1   ==> A new line
     @ Line 3 in file "list1" is shorter than expected!

   In addition, 'numdiff' shows the tail of the longer line, using the
notation "#>n" to indicate the number n of the first field of the longer
line for which there is no corresponding field in the shorter line.  For
example,
     ##1       #>6   <== water
     ##1             ==>
     @ Line 1 in file "list2" is shorter than expected!

means that none of the fields of the first line starting from the sixth
one has a corresponding field in the second file ('list2').  In this
context, the symbol <<*>> (if it appears) is used to denote the
End-Of-File, i.e.  a line or the tail of a line which is located at the
end of the corresponding file and does not have a terminating _newline_
character.

   It can also happen that one of the two files to compare has less
lines than the other one.  In this case, if no special option is passed
to the program, 'numdiff' prints the number of the first line which
appears in only one of the two files and a message on the standard error
telling in which of the two files the end has been prematurely reached:
     ***  End of file "list1" reached while trying to read line 4.
          File "list2" has more lines than file "list1",
          line 4 is the last one read from file "list2"

   Unless the option '-q' is used (*note Invoking numdiff::), 'numdiff'
prints to the standard output a message reporting the final status of
the comparison.  This message says either the two files are equal or
they are different, just as in the example we are considering:
     +++  File "list1" differs from file "list2"

3.2 Overview mode
=================

Since version 5.6 an alternative way to display the differences between
two files is available, which can be activated through the option '-O'.
If this option is present on the command line, 'numdiff' prints a
side-by-side report instead of the usual one.

   For example, if 'sheet1' contains the text
A    1    1
B    2    4
C    3    9
D    4   16
E    5   25
F    6   36
G    7   49
H    8   64
I    9   81
J   10  100

and 'sheet2' the following lines

A    1      1
B    2      4
C    3.3    9.03
D    4     16
E    5.5   25.05
F    6.6   36
G    7.7   49.49
H    8     64
I    9.9   81.09

then 'numdiff -O sheet1 sheet2' prints this report
     A    1    1                            A    1      1
     B    2    4                            B    2      4
     C    3    9                         :!:C    3.3    9.03
     D    4   16                            D    4     16
     E    5   25                         :!:E    5.5   25.05
     F    6   36                         :!:F    6.6   36
     G    7   49                         :!:G    7.7   49.49
     H    8   64                            H    8     64
     I    9   81                         :!:I    9.9   81.09
     J   10  100                         :<:

     ***  End of file "sheet2" reached while trying to read line 10.
          File "sheet1" has more lines than file "sheet2",
          line 10 is the last one read from file "sheet1"


     +++  File "sheet1" differs from file "sheet2"

   On the left side you can see the lines coming from the file specified
as first on the command line, i.e.  'sheet1', on the right side the
lines from the second file of the command line, in this case 'sheet2'.
In the middle there is a gutter which contains one of these markers:
'white spaces'
     The corresponding lines are in common.  That is, either the lines
     are identical, or the difference is ignored because of one of the
     options '-s', '-D', '-I', '-X', '-a', '-r', '-P', or '-N'.

':!:'
     The corresponding lines have at least one field which differs.

':<:'
     The files differ and only the first file contains the line.

':>:'
     The files differ and only the second file contains the line.

   In the case of 'sheet1' and 'sheet2' a message is printed after the
report saying that the end of the second file has been prematurely
reached.  The two files do not have indeed the same number of lines and
the filter has not been activated.

   The option '-O' can take an optional argument, which allows to set
the width of the output and eventually to suppress common lines, *note
Invoking numdiff::.  The default value for the width of the side-by-side
report is 130.  No wonder then that the command 'numdiff -O40 sheet1
sheet2' displays a report with shorter lines:
     A    1    1           A    1      1
     B    2    4           B    2      4
     C    3    9       :!: C    3.3    9.03
     D    4   16           D    4     16
     E    5   25       :!: E    5.5   25.05
     F    6   36       :!: F    6.6   36
     G    7   49       :!: G    7.7   49.49
     H    8   64           H    8     64
     I    9   81       :!: I    9.9   81.09
     J   10  100       :<:

     ***  End of file "sheet2" reached while trying to read line 10.
          File "sheet1" has more lines than file "sheet2",
          line 10 is the last one read from file "sheet1"


     +++  File "sheet1" differs from file "sheet2"

   A negative argument makes that only the differences are listed in the
side-by-side report, as shown by the output of the command 'numdiff -O40
sheet1 sheet2':
     C    3    9       :!: C    3.3    9.03
     E    5   25       :!: E    5.5   25.05
     F    6   36       :!: F    6.6   36
     G    7   49       :!: G    7.7   49.49
     I    9   81       :!: I    9.9   81.09
     J   10  100       :<:

     ***  End of file "sheet2" reached while trying to read line 10.
          File "sheet1" has more lines than file "sheet2",
          line 10 is the last one read from file "sheet1"


     +++  File "sheet1" differs from file "sheet2"

   If you set the width of the report to a too small value, it can
happen that some or even all lines from the compared files appear
truncated as in the output of 'numdiff -O24 sheet1 sheet2':
     A    1         A    1
     B    2         B    2
     C    3    :!:  C    3.3
     D    4         D    4
     E    5    :!:  E    5.5
     F    6    :!:  F    6.6
     G    7    :!:  G    7.7
     H    8         H    8
     I    9    :!:  I    9.9
     J   10    :<:

     ***  End of file "sheet2" reached while trying to read line 10.
          File "sheet1" has more lines than file "sheet2",
          line 10 is the last one read from file "sheet1"


     +++  File "sheet1" differs from file "sheet2"

   If you set the width of the report to a very small value, Numdiff
ignores it and uses the default value, i.e.  130.

   Notice that the numeric argument must immediately follow the option
'-O', intermediate spaces are not allowed.  This is also the case for
the optional argument of '-f', while the options of Numdiff which
require a mandatory argument permit the presence of intermediate spaces
between them and the argument.

   The option '-O' can be used together with any other option of Numdiff
except for '-f', '-q', '-U', '-E', '-V' and '-b'.  When '-O' is in use,
'-U', '-E', '-V' and '-b' are ignored.  If '-q' is present on the
command line together with '-O', then '-O' is ignored.  Finally, if both
'-f' and '-O' are present, then the behavior depends on the order: the
option which appears first on the command line is the one which matters.

   Therefore, the command 'numdiff -O40 -f sheet1 sheet2' displays the
same report as 'numdiff -O40 sheet1 sheet2', while the output of
'numdiff -f -O40 sheet1 sheet2' is given by
     A    1    1                            A    1      1
     B    2    4                            B    2      4
     C    3    9                          | C    3.3    9.03
     D    4   16                            D    4     16
     E    5   25                          | E    5.5   25.05
     F    6   36                          | F    6.6   36
     G    7   49                          | G    7.7   49.49
     H    8   64                            H    8     64
     I    9   81                          | I    9.9   81.09
     J   10  100                          <


     +++  File "sheet1" differs from file "sheet2"

and coincides then with the output of 'numdiff -f sheet1 sheet2'.

   The option '-O' can be used together with the filter to cope with the
addition/deletion of lines.  If the file 'sheet3' contains the text
A    1      1
C    3.3    9.03
E    5.5   25.05
G    7.7   49.49
I    9.9   81.09
J    10   100.00
K    0      0.02

then 'numdiff -O40 sheet1 sheet3' prints a wrong report, as in the
example with files 'bill1' and 'bill2':
     A    1    1           A    1      1
     B    2    4     :!:   C    3.3    9.03
     C    3    9     :!:   E    5.5   25.05
     D    4   16     :!:   G    7.7   49.49
     E    5   25     :!:   I    9.9   81.09
     F    6   36     :!:   J    10   100.00
     G    7   49     :!:   K    0      0.02
     H    8   64     :<:

     ***  End of file "sheet3" reached while trying to read line 8.
          File "sheet1" has more lines than file "sheet3",
          line 8 is the last one read from file "sheet1"


     +++  File "sheet1" differs from file "sheet3"

   On the other hand, the presence of '-z @' makes Numdiff always
compare fields of corresponding lines, as shown by the output of the
command 'numdiff -O40 -z @ sheet1 sheet3':
     A    1    1           A    1      1
     B    2    4     :<:
     C    3    9     :!:   C    3.3    9.03
     D    4   16     :<:
     E    5   25     :!:   E    5.5   25.05
     F    6   36     :<:
     G    7   49     :!:   G    7.7   49.49
     H    8   64     :<:
     I    9   81     :!:   I    9.9   81.09
     J   10  100           J    10   100.00
                     :>:   K    0      0.02

     +++  File "sheet1" differs from file "sheet3"

   Side-by-side format is easy to read, but it has limitations.  It
generates much wider output than usual, and truncates lines that are too
long to fit.  Also, it relies on lining up output quite heavily, so its
output looks particularly bad if you use varying width fonts,
nonstandard tab stops, or nonprinting characters.

3.3 Output of the filter
========================

The output produced just by running the filter (option '-f') is a
side-by-side difference listing of the compared files like the one
displayed by GNU sdiff.  The files are listed in two columns with a
gutter between them.  The gutter contains one of the following markers:
'white space'
     The corresponding lines are in common.  That is, either the lines
     are identical, or the difference is ignored because of one of the
     options '-s', '-D', '-I', '-X', '-z', or '-Z'.

'|'
     The corresponding lines differ, and they are either both complete
     or both incomplete.

'<'
'('
     The files differ and only the first file contains the line.

'>'
')'
     The files differ and only the second file contains the line.

'\'
     The corresponding lines differ, and only the first line is
     incomplete.

'/'
     The corresponding lines differ, and only the second line is
     incomplete.

   An input line is incomplete if its last character is not a newline.
This can happen only if the line is the last one of its file.  When an
output line of the side by side difference listing represents two
differing lines, one might be incomplete while the other is not.  In
this case the gutter is marked '\' if the line from the first file is
incomplete, '/' if the line from the second file is it.

   Like '-O', the option '-f' can take an optional argument which allows
to set the width of the output and eventually to suppress common lines,
*note Invoking numdiff:: and *note Use of the option -f::.

   More generally, the user can always make 'numdiff' avoid to print,
partially or totally, the messages that it would otherwise send to
standard output.  This can be achieved by some suitable command line
options, *note Invoking numdiff::.

3.4 Raw output
==============

Since version 5.9 Numdiff can report the results of the comparison of
two files in a particularly compact format, which can be easily parsed
by other programs.  This _raw_ format is chosen by Numdiff whenever the
user requests it through the command line option '--raw'.  Below you can
see an example of raw output in the case of the comparison of the files
'list1' and 'list2' from section *note Output format:::
     1:1:1:1:*:*:accident ==> Accident
     1:1:3:3:*:*:23Joshua ==> 23456
     1:1:5:5:1.0000000000e-4:2.0000000000e-5:+3+4i ==> +3.0001+4i
     1:1:6:*:water
     2:2:2:2:9.0200000000e-4:2.6104672633e-7:-3455.321 ==> -3455.320098
     2:2:3:3:*:*:cat ==> Cat
     2:2:5:5:5.0000000000e-4:8.0256821830e-7:.0005-6.23e2i ==> -6.23e2i
     2:2:*:6:$$$
     3:3:*:1:A new line
     *:4

     +++  File "list1" differs from file "list2"

   The raw format is not at all convenient for humans.  It has been
provided only for being used by the forthcoming graphic user interface
of Numdiff (yes, Numdiff will have a GUI sometime in the future!).

4 Installing
************

To successfully compile, build and install Numdiff some tools are
required.  The first one is an ANSI C compiler.  This compiler should at
least accept the option '-o' to write its output to a specified file,
the option '-D' for macros predefinition, the option '-l' to search for
a specified library, and the options '-I' and '-L' to add a given
directory to the search path for include and library files respectively.

   In addition, you need a POSIX implementation of the 'make' utility (I
used both GNU make and smake by Joerg Schilling to compile Numdiff) and
a POSIX implementation of the commands 'rm' and 'find'.  At last, you
need a proper installation of GNU Texinfo (in order to install the info
documentation) and a shell sh-compatible.

   Numdiff has been successfully compiled and tested on:

   * Slackware(R) GNU/Linux 10.2 with the version 3.3.6 of the GNU C
     Compiler (GCC),
   * Slackware GNU/Linux 11 with GCC 3.4.6,
   * Slackware GNU/Linux 12.2 with GCC 4.2.4,
   * Slackware GNU/Linux 13 with GCC 4.3.3,
   * Debian(R) GNU/Linux 4.0 with GCC 4.1.2 20061115 (prerelease)
     (Debian 4.1.1-21),
   * Debian GNU/Linux 6.0.3 with GCC 4.4.5 (Debian 4.4.5-8),
   * Debian GNU/Linux 7.1 with GCC 4.7.2 (Debian 4.7.2-5),
   * Debian GNU/Linux 8.6 with GCC 4.9.2 (Debian 4.9.2-10),
   * SunOS(R) 5.8 with GCC 2.95.3, and
   * SunOS 5.10 (i386) with the version 5.9 of the Sun C compiler.

   Configuration, building and installation of Numdiff can be performed
through the standard three steps:
             ./configure
             make
             make install

If you leave enabled the Natural Language Support and you also want to
install the localization files (at the moment only the Italian
localization is supplied), then after 'make' you will have to type and
run
             make install-nls

   By default, 'make install' will install all the files in
'/usr/local/bin', '/usr/local/info' etc.  You can specify an
installation prefix other than '/usr/local' using the option '--prefix'
in the 'configure' step, for instance '--prefix=$HOME':
             ./configure --prefix=$HOME

For better control, you can use the options '--bindir', '--infodir', and
so on.  Type './configure --help' to obtain the complete list of all
available options.

   The documentation files (including a full User Manual available in
HTML, PDF and plain ASCII text format) will always be put in
'DOCDIR/numdiff', where DOCDIR is the path specified by the option
'--docdir' or, if this option has not been given to 'configure',
'PREFIX/local/doc'.  Here PREFIX is the installation prefix specified by
the option '--prefix' or the default '/usr/local'.

   Once Numdiff has been installed you can remove all files related to
Numdiff by a simple 'make uninstall'.  If you have also installed the
localization files trough 'make install-nls', use 'make uninstall-nls'
in place of 'make uninstall' to remove them too.

   Between the options accepted by 'configure' there are
'--enable-debug', '--enable-optimization', '--enable-nls' and
'--enable-gmp'.

   The option '--enable-debug' turns on debugging when compiling the
source code.  This is obtained by passing to the compiler the '-g'
option, but you can change this default debugging flag (which could not
even be recognized by your compiler) by setting the environment variable
'DBGFLAGS' before launching 'configure'.

   The option '--enable-optimization' turns on basic optimization when
compiling the source code.  This is obtained by passing to the compiler
the '-O' option, but you can change this default flag (which could not
even be recognized by your compiler) by setting the environment variable
'OPTFLAGS' before launching 'configure'.

   The option '--enable-nls' turns on Natural Language Support.  You do
not need to use it explicitly since Natural Language Support is enabled
by default.  To disable it, use '--disable-nls'.  Disabling Natural
Language Support is suggested whenever you want to install Numdiff on a
system where the GNU gettext library is not present.  In this case the
installation of Numdiff can be accomplished, for example, through
             ./configure --disable-nls
             make
             make install

Since version 5.2.0 Numdiff uses to perform all computations the GNU
Multiple Precision Arithmetic Library (also called GNU MP or GMP), if
this library is available at build-time.  The old internal support for
multiple precision arithmetic is a fall-back in case GNU MP is absent.
However, it is possible to use the internal support for multiple
precision arithmetic even if GNU MP is available: it is sufficient to
pass the option '--enable-gmp=no' or '--disable-gmp' to the configure
script before building the program, like in
             ./configure --disable-gmp
             make
             make install

Enabling the old internal support for multiple precision arithmetic is
deprecated, *note with GNU MP is better::.  The latest version of GNU MP
is available at <http://ftp.gnu.org/gnu/gmp/>.  See the GNU MP web page
at <http://gmplib.org/> for up-to-date information on GNU MP.

5 Invoking numdiff
******************

*SYNOPSIS*

        numdiff -h|--help|-v|--version
   or
        numdiff [-s IFS][-D DELIMS][-a THRVAL[:RANGE|:RANGE1:RANGE2]]
        [-r THRVAL[:RANGE|:RANGE1:RANGE2]][-2][-F NUM][-# NUM][-P][-N][-I]
        [-c CURRNAME][-d C1C2][-t C1C2][-g N1N2][-p C1C2][-n C1C2][-e C1C2]
        [-i C1C2][-X 1:RANGE][-X 2:RANGE][-E][-U][-b][-V][-O[NUM]][--raw][-q][-S]
        [-z 1:RANGE][-z 2:RANGE][-Z 1:RANGE][-Z 2:RANGE][-m][-H][-f[NUM]]
        [-T][-B][-l PATH][-o PATH] FILE1 FILE2

where FILE1 and FILE2 are the names of the two files to compare and
RANGE, RANGE1 and RANGE2 stay for a positive integer value or for a
range of integer values, like '1-', '3-5' or '-7'.

   In the first case 'numdiff' prints a short help (not so short
actually :)) or/and version number, Copyright, License notice,
NO-Warranty disclaimer, and some information about the way it was built.
In the second case 'numdiff' compares the files specified by the two
mandatory arguments which follow the list of the options.  The complete
paths of the files should be given, a directory name is not accepted.
In addition, the two arguments cannot refer to the same file but one of
them can be -, which refers to stdin.

*OPTIONS*

'-s, --separators=IFS'
     Specify the set of characters to use as delimiters while splitting
     the input lines into fields (The default set of delimiters is
     space, tab and newline).  If IFS is prefixed with '1:' or '2:', use
     the given delimiter set only for the lines from the first or the
     second file respectively

'-D, --delimiters=DELIMS'
     Specify the set of strings to use as delimiters while splitting the
     input lines into fields (The default set of delimiters is space,
     tab and newline).  If DELIMS is prefixed with '1:' or '2:', use the
     given delimiter set only for the lines from the first or the second
     file respectively

'-a, --absolute-tolerance=THRVAL[:RANGE|:RANGE1:RANGE2]'
     Set to THRVAL the maximum absolute difference permitted before two
     numeric fields are regarded as different (The default value is
     zero).  If a RANGE is given, use the specified threshold only when
     comparing fields whose indexes lie in RANGE.  If both RANGE1 and
     RANGE2 are given and have the same length, then use the specified
     threshold when comparing a field of FILE1 lying in RANGE1 with the
     corresponding field of FILE2 in RANGE2

'-r, --relative-tolerance=THRVAL[:RANGE|:RANGE1:RANGE2]'
     Set to THRVAL the maximum relative difference permitted before two
     numeric fields are regarded as different (The default value is
     zero).  If a RANGE is given, use the specified threshold only when
     comparing fields whose indexes lie in RANGE.  If both RANGE1 and
     RANGE2 are given and have the same length, then use the specified
     threshold when comparing a field of FILE1 lying in RANGE1 with the
     corresponding field of FILE2 in RANGE2

'-2, --strict'
     Consider two numerical values as equal only if both absolute and
     relative difference do not exceed the respective tolerance
     threshold

'-F, --formula=NUM'
     Use the formula indicated by NUM to compute the relative errors.
     If NUM is 0 use the classic formula.  If NUM is 1 compute the
     relative errors by considering the values in FILE1 as sample
     values.  If NUM is 2 compute the relative errors by considering the
     values in FILE2 as sample values.

'-#, --digits=NUM'
     Set to NUM the number of digits in the significands used in
     multiple precision arithmetic

'-P, --positive-differences'
     Ignore all differences due to numeric fields of the second file
     that are less than the corresponding numeric fields in the first
     file

'-N, --negative-differences'
     Ignore all differences due to numeric fields of the second file
     that are greater than the corresponding numeric fields in the first
     file

'-I, --ignore-case'
     Ignore changes in case while doing literal comparisons

'-c, --currency=CURRNAME'
     Set to CURRNAME the currency name for the two files to compare.
     CURRNAME must be prefixed with '1:' or '2:' to specify the currency
     name only for the first or the second file

'-d, --decimal-point=C1C2'
     Specify the characters representing the decimal point in the two
     files to compare

'-t, --thousands-separator=C1C2'
     Specify the characters representing the thousands separator in the
     two files to compare

'-g, --group-length=N1N2'
     Specify the number of digits forming each group of thousands in the
     two files to compare

'-p, --plus-prefix=C1C2'
     Specify the (optional) prefixes for positive values used in the two
     files to compare

'-n, --minus-prefix=C1C2'
     Specify the prefixes for negative values used in the two files to
     compare

'-e, --exponent-letter=C1C2'
     Specify the exponent letters used in the two files to compare

'-i, --imaginary-unit=C1C2'
     Specify the characters representing the imaginary unit in the two
     files to compare

'-X, --exclude=1:RANGE'
     Select the fields of the first file that have to be ignored

'-X, --exclude=2:RANGE'
     Select the fields of the second file that have to be ignored

'-E, --essential'
     While printing the differences between the two compared files show
     only the numerical ones

'-U, --dummy'
     While printing the differences between the two compared files
     neglect all the numerical ones (dummy mode)

'-b, --brief'
     Suppress all messages concerning the differences discovered in the
     structures of the two files

'-V, --verbose'
     For every couple of lines which differ in at least one field print
     an header to show how these lines appear in the two compared files

'-O, --overview[=NUM]'
     Display a side by side difference listing of the two files showing
     which lines are present only in one file, which lines are present
     in both files but with one or more differing fields, and which
     lines are identical.  If NUM is zero or is not specified, output at
     most 130 columns per line.  If NUM is a positive number, output at
     most NUM columns per line.  If NUM is a negative number, do not
     output common lines and display at most -NUM columns per line.

'--raw'
     Display the differences between the two compared files in raw
     format (not very convenient for humans)

'-q, --quiet, --silent'
     Suppress all the standard output

'-S, --statistics'
     Add some statistics to the standard output

'-z, --blur-if-numerical=1:RANGE'
     Select the fields of the first file that have to be blurred during
     the synchronization procedure only if they turn out to be numeric

'-z, --blur-if-numerical=2:RANGE'
     Select the fields of the second file that have to be blurred during
     the synchronization procedure only if they turn out to be numeric

'-Z, --blur-unconditionally=1:RANGE'
     Select the fields of the first file that have to be unconditionally
     blurred during the synchronization procedure

'-Z, --blur-unconditionally=2:RANGE'
     Select the fields of the second file that have to be
     unconditionally blurred during the synchronization procedure

'-m, --minimal'
     During synchronization try hard to find a smaller set of changes

'-H, --speed-large-files'
     During synchronization assume large files and many scattered small
     changes

'-f, --test-filter[=NUM]'
     Run only the filter and then show the results of its attempt to
     synchronize the two files.  If NUM is zero or is not specified,
     output at most 130 columns per line.  If NUM is a positive number,
     output at most NUM columns per line.  If NUM is a negative number,
     do not output common lines and display at most -NUM columns per
     line.

'-T, --expand-tabs'
     Expand tabs to spaces in output while displaying the results of the
     synchronization procedure (meaningful only together with option
     '-O' or '-f')

'-B, --binary'
     Treat both files as binary files (only meaningful under Doz/Windoz)

'-l, --warnings-to=PATH'
     Redirect warning and error messages from stderr to the indicated
     file

'-o, --output=PATH'
     Redirect output from stdout to the indicated file

'-h, --help'
     Show help message and predefined settings

'-v, --version'
     Show version number, Copyright, Distribution Terms and NO-Warranty

*DIAGNOSTICS*

   The exit status is 1 if the two given files differ, 0 if they are
equal, -1 (255) in case of error.

*DEFAULT NUMERIC FORMAT (for both files to compare):*

   Currency name = ""

   Decimal point = '.'

   Thousands separator = ','

   Number of digits in each thousands group = 3

   Leading positive sign = '+'

   Leading negative sign = '-'

   Prefix for decimal exponent = 'e'

   Symbol used to denote the imaginary unit = 'i'

*SOME EXPLANATIONS*

   The options '-U', '-E', '-b', and '-q' are used to hide part of the
standard output of the program according to certain rules.

   The option '-U' triggers the dummy mode.  In this mode 'numdiff' does
not print the numerical differences.  A numerical difference occurs
whenever the compared fields turn out to be both of numerical type, but
the field from the second file has a value which differs from the one of
the field from the first file.  The dummy mode is so called since in
this mode 'numdiff' does not perform the job for which I created it.

   The option '-E' triggers the essential mode.  In this mode 'numdiff'
only prints the numerical differences between the files and, if there
are some, the differences in the structure.  The latter ones occur
either when one of the files contains a line for which there is no
corresponding line in the other file, or when the comparison of
corresponding lines shows that one of them contains a field for which
there exists no corresponding field in the other line.  If you are not
running any filter or cutting out any fields through the option '-X',
then the differences in the structure simply consist either in a
different number of lines in the two files, or in a different number of
fields on a line.

   The option '-b' triggers the brief mode.  In this mode 'numdiff' does
not print the differences in the structure of the two files (see above
for an explanation about what differences in the structure are).

   The option '-q' triggers the quiet mode.  In this mode 'numdiff' does
not print anything on the standard output.  The quiet mode is useful if
you only want to know whether a couple of files are equal or not.  This
information can be obtained by looking at the exit status of the
program.

   The option '-O' activates the overview mode, which makes 'numdiff'
print a side-by-side report in the form described in section *note
Overview mode::.  The optional numeric argument after '-O' must
immediately follow, intermediate spaces are not allowed.  The option
'-O' can be used together with any other option of Numdiff except for
'-f', '-q', '-U', '-E', '-V', '-b', and '--raw'.  Whenever '-O' is in
use, '-U', '-E', '-V' and '-b' are ignored.  If '--raw' or '-q' is
present on the command line together with '-O', then '-O' is ignored.
Finally, if both '-f' and '-O' are present, the behavior of Numdiff will
depend on their order: the option which appears first on the command
line is the one which matters.

   The option '-V' triggers the verbose mode.  In this mode 'numdiff'
produces a richer report by printing an header whenever the compared
lines differ.  The header shows how and where these lines appear in the
compared files.  For instance, if the files 'data1' and 'data2' contain
the data
12      33
22      44.5
0.008   1.002
221.12  -34.56  water
2101.21 boats

and

12      33
22.3      44.5
0.008   1.202
221.12  -34.56
2101.21 boats   dogs

respectively, then the command 'numdiff -V data1 data2' will print the
following output:
     ----------------
     ##2       <== 22      44.5
     ##2       ==> 22.3      44.5

     ##2       #:1   <== 22
     ##2       #:1   ==> 22.3
     @ Absolute error = 3.0000000000e-1, Relative error = 1.3636363636e-2
     ----------------
     ##3       <== 0.008   1.002
     ##3       ==> 0.008   1.202

     ##3       #:2   <== 1.002
     ##3       #:2   ==> 1.202
     @ Absolute error = 2.0000000000e-1, Relative error = 1.9960079840e-1
     ----------------
     ##4       <== 221.12  -34.56  water
     ##4       ==> 221.12  -34.56

     ##4       #>3   <== water
     ##4             ==>
     @ Line 4 in file "data2" is shorter than expected!
     ----------------
     ##5       <== 2101.21 boats
     ##5       ==> 2101.21 boats   dogs

     ##5             <==
     ##5       #>3   ==> dogs
     @ Line 5 in file "data1" is shorter than expected!

     +++  File "data1" differs from file "data2"

   Mind that the options '-b' and '-V' will be overridden if '-q' is
also set.

   The amount of additional information printed by '-V' is trivially
influenced by the options that alter the way 'numdiff' performs the
comparisons between fields (for instance '-a', '-r', '-2', '-N', '-P',
'-U', '-E', '-I', '-X').

   In the headers printed by 'numdiff' in "verbose mode" the symbol
<<*>> can appear.  This symbol, if present, is always located at the end
of a line to mean that the line is at the end of the corresponding file
and does not have a terminating *newline* character.

   The option '-S' adds to the standard output of 'numdiff' a
statistical report with the following information:
   * the number of numeric comparisons the program has done (this
     quantity, like the successive ones, is influenced by the options
     '-P' and '-N') and the number of those ones whose outcome is a
     major (1) numerical difference.
   * the largest absolute error in the set of major numerical
     differences together with the corresponding relative error, and the
     positions of its first occurrences in the compared files,
   * the largest relative error in the set of major numerical
     differences together with the corresponding absolute error, and the
     positions of its first occurrences in the compared files,
   * the sum and the arithmetic mean of all absolute errors,
   * the sum and the arithmetic mean of the major absolute errors,
   * the square root of the sum of the squares of all absolute errors,
   * the square root of the sum of the squares of the major absolute
     errors,
   * the quadratic mean of all absolute errors, and
   * the quadratic mean of the major absolute errors.
   The information printed by '-S' is not removed if this option is used
together with '-q', and is not influenced by the option '--raw'.

   The options '-a', '-r', '-2', '-P' and '-N' affect the way 'numdiff'
performs the comparisons between numerical values.  Without any of these
options, 'numdiff' considers two numerical fields as equal if their
difference is zero.

   The option '-a' can be used to make two numerical fields be
considered equal as long as their absolute difference does not exceed a
certain threshold, which is specified by the argument that follows the
'-a' option.  This argument can take several forms.  The basic form
consists of a single numerical value, the extended form adds the
specification of one or two ranges of integer values.

   Independently of the form of the argument, if the absolute difference
between two fields does not exceed the given threshold value, the fields
are considered equal; otherwise, 'numdiff' prints the difference in its
report, unless some other option, for example '-P' or '-N', makes the
difference be neglected.  If nothing else follows the threshold value,
the rule just explained applies to all comparisons between numerical
fields.  To see this in practice, if the file 'many_columns1' contains
the text
A	1	 1.2	  1	 0.1	  11.0         1.0e-1
B	2        2.4      4      0.4      24.0         1.0e-2
C	3        3.6      9      0.9      39.0         1.0e-3
D	4	 4.8     16      1.6     416.0         1.0e-4

and the contents of the file 'many_columns2' are given by

A	1.1	1.08	 1.01	 0.1	 11.011        -1.0e-1
B	2.2     2.16     4.04    0.4     24.024        -1.0e-2
C	3.3     3.24     9.09    0.9     39.039        -1.0e-3
D	4.4	4.32    16.16    1.6    416.039        -1.0e-4

then the output of the command 'numdiff -a 0.5 many_columns1
many_columns2' will be

     +++  Files "many_columns1" and "many_columns2" are equal

The highest absolute difference between a field from 'many_columns1' and
the corresponding field from 'many_columns2' is given indeed by |4.32 -
4.8| = |-0.48| = 0.48, and then all numeric differences between the two
files remain below the threshold value 0.5.

   On the other hand, the command 'numdiff -a 0.35 many_columns1
many_columns2' prints the report
     ----------------
     ##3       #:3   <== 3.6
     ##3       #:3   ==> 3.24
      Absolute error = 3.6000000000e-1, Relative error = 1.1111111111e-1
     ----------------
     ##4       #:2   <== 4
     ##4       #:2   ==> 4.4
      Absolute error = 4.0000000000e-1, Relative error = 1.0000000000e-1
     ##4       #:3   <== 4.8
     ##4       #:3   ==> 4.32
      Absolute error = 4.8000000000e-1, Relative error = 1.1111111111e-1

     +++  File "many_columns1" differs from file "many_columns2"

since the absolute differences |3.24-3.6| = |-0.36| = 0.36, |4.4-4| =
|0.4| = 0.4, and |4.32 - 4.8| = 0.48 exceed the value 0.35, while the
other differences are below this threshold.

   If you want that the specified threshold value applies only when
comparing some particular fields, you have to use the extended form for
the argument of '-a'.  This means that after the threshold value one or
two ranges of integer numbers must follow, each preceded by a colon
(':').  If you specify only one range of numbers after the threshold
value, 'numdiff' uses the given threshold only when comparing fields
whose positions lie in the specified range.  Remember that the positions
of the fields on a line are numbered starting from the left hand of the
line and proceeding towards the right hand.  For example, '-a 0.01:2-5'
sets the threshold value to 0.01 only for the comparisons between
numerical fields which occupy on their lines a position between the
second and the fifth one inclusive.  For the other comparisons the
threshold value is left unchanged; in particular, it is equal to zero if
it has not been explicitly set.  If the files 'many_columns1' and
'many_columns2' are the same as before, then the command 'numdiff -a
0.5:3-6 many_columns1 many_columns2' will display the following report
     ----------------
     ##1       #:2   <== 1
     ##1       #:2   ==> 1.1
      Absolute error = 1.0000000000e-1, Relative error = 1.0000000000e-1
     ##1       #:7   <== 1.0e-1
     ##1       #:7   ==> -1.0e-1
      Absolute error = 2.0000000000e-1, Relative error = 2.0000000000e+0
     ----------------
     ##2       #:2   <== 2
     ##2       #:2   ==> 2.2
      Absolute error = 2.0000000000e-1, Relative error = 1.0000000000e-1
     ##2       #:7   <== 1.0e-2
     ##2       #:7   ==> -1.0e-2
      Absolute error = 2.0000000000e-2, Relative error = 2.0000000000e+0
     ----------------
     ##3       #:2   <== 3
     ##3       #:2   ==> 3.3
      Absolute error = 3.0000000000e-1, Relative error = 1.0000000000e-1
     ##3       #:7   <== 1.0e-3
     ##3       #:7   ==> -1.0e-3
      Absolute error = 2.0000000000e-3, Relative error = 2.0000000000e+0
     ----------------
     ##4       #:2   <== 4
     ##4       #:2   ==> 4.4
      Absolute error = 4.0000000000e-1, Relative error = 1.0000000000e-1
     ##4       #:7   <== 1.0e-4
     ##4       #:7   ==> -1.0e-4
      Absolute error = 2.0000000000e-4, Relative error = 2.0000000000e+0

     +++  File "many_columns1" differs from file "many_columns2"

since the threshold value 0.5 applies now only when comparing fields in
third, fourth, fifth and sixth position, while for the other comparisons
the threshold value is the default one, i.e.  zero.  If you want to
specify a non null threshold also for the fields in second and seventh
position, you can do it by using the option '-a' more times.  The
command 'numdiff -a 0.5:3-6 -a 0.25:2 -a 4e-3:7 many_columns1
many_columns2' sets the threshold value to 0.25 for the comparisons
between the fields in second position, and to 4e-3 for the comparisons
of the fields in seventh position.  No wonder then, that the command
prints exactly this report:
     ----------------
     ##1       #:7   <== 1.0e-1
     ##1       #:7   ==> -1.0e-1
      Absolute error = 2.0000000000e-1, Relative error = 2.0000000000e+0
     ----------------
     ##2       #:7   <== 1.0e-2
     ##2       #:7   ==> -1.0e-2
      Absolute error = 2.0000000000e-2, Relative error = 2.0000000000e+0
     ----------------
     ##3       #:2   <== 3
     ##3       #:2   ==> 3.3
      Absolute error = 3.0000000000e-1, Relative error = 1.0000000000e-1
     ----------------
     ##4       #:2   <== 4
     ##4       #:2   ==> 4.4
      Absolute error = 4.0000000000e-1, Relative error = 1.0000000000e-1

     +++  File "many_columns1" differs from file "many_columns2"

Observe that :2 and :7 are abbreviations of :2-2 and :7-7, respectively.
It is even possible to use range expressions like 'M-' or '-N'.  The
first expression means all fields starting from the Mth one (inclusive)
till to the end of line, the second selects all fields from the first
one till to the Nth one, both inclusive.

   If you specify two ranges of numbers after the threshold value and
they have the same length (the length of a range is the difference
between its maximum and its minimum), 'numdiff' uses the given threshold
when comparing a field of the first file lying in the first range with
the corresponding field of the second file from the second range.  For
example, '-a 1e-4:3-5:4-6' sets the threshold value to 0.0001 only for
the numerical comparisons of the third, fourth, and fifth field of each
line from the first file with the fourth, fifth and sixth field
respectively of the corresponding line from the second file.  For the
other comparisons the threshold value is left unchanged and is in
particular equal to zero if it has not been explicitly set.  This way to
restrict the application of a threshold value is useful in conjunction
with the option '-X', which makes 'numdiff' ignore one or more fields
from one of the compared files.

   The file 'many_columns3':
A    I	1.1	1.08	 1.01	 0.1	 11.011        -1.0e-1
B   II	2.2     2.16     4.04    0.4     24.024        -1.0e-2
C  III	3.3     3.24     9.09    0.9     39.039        -1.0e-3
D   IV	4.4	4.32    16.16    1.6    416.039        -1.0e-4

has one column more than the file 'many_columns1', namely the second
one.  When comparing 'many_columns1' with 'many_columns3' it is natural
then to ignore the second column of the second file.  This can be
achieved by passing the argument 2:2 to the option '-X' (for a full
description of the use of this option, *note Restriction of the
comparison to particular fields::).  Ignoring the second field of each
line of 'many_columns3' implies that the fields in the third column of
this file are compared with the corresponding fields of the second
column of 'many_columns1', the fields in the fourth column of
'many_columns3' are compared with the ones in the third column of
'many_columns1', and so on.  Therefore, if you want to set a threshold
value only for the comparisons between some particular fields you have
to consider that '-X 2:2' makes 'numdiff' compare the first, second,
third, fourth, fifth, sixth, and seventh field of each line of
'many_columns1' with the first, third, fourth, fifth, sixth, seventh,
and eighth field respectively of the corresponding line of
'many_columns3'.  Therefore, the command 'numdiff -X 2:2 -a 0.5:3-6
many_columns1 many_columns3' will use 0.5 as threshold value only when
comparing the third, fourth, and fifth field of a line from
'many_columns1' with the fourth, fifth, and sixth field respectively of
the corresponding line of 'many_columns3'.  This explains why the report
of 'numdiff -X 2:2 -a 0.5:3-6 many_columns1 many_columns3'
     ----------------
     ##1       #:2   <== 1
     ##1       #:3   ==> 1.1
      Absolute error = 1.0000000000e-1, Relative error = 1.0000000000e-1
     ##1       #:6   <== 11.0
     ##1       #:7   ==> 11.011
      Absolute error = 1.1000000000e-2, Relative error = 1.0000000000e-3
     ##1       #:7   <== 1.0e-1
     ##1       #:8   ==> -1.0e-1
      Absolute error = 2.0000000000e-1, Relative error = 2.0000000000e+0
     ----------------
     ##2       #:2   <== 2
     ##2       #:3   ==> 2.2
      Absolute error = 2.0000000000e-1, Relative error = 1.0000000000e-1
     ##2       #:6   <== 24.0
     ##2       #:7   ==> 24.024
      Absolute error = 2.4000000000e-2, Relative error = 1.0000000000e-3
     ##2       #:7   <== 1.0e-2
     ##2       #:8   ==> -1.0e-2
      Absolute error = 2.0000000000e-2, Relative error = 2.0000000000e+0
     ----------------
     ##3       #:2   <== 3
     ##3       #:3   ==> 3.3
      Absolute error = 3.0000000000e-1, Relative error = 1.0000000000e-1
     ##3       #:6   <== 39.0
     ##3       #:7   ==> 39.039
      Absolute error = 3.9000000000e-2, Relative error = 1.0000000000e-3
     ##3       #:7   <== 1.0e-3
     ##3       #:8   ==> -1.0e-3
      Absolute error = 2.0000000000e-3, Relative error = 2.0000000000e+0
     ----------------
     ##4       #:2   <== 4
     ##4       #:3   ==> 4.4
      Absolute error = 4.0000000000e-1, Relative error = 1.0000000000e-1
     ##4       #:6   <== 416.0
     ##4       #:7   ==> 416.039
      Absolute error = 3.9000000000e-2, Relative error = 9.3750000000e-5
     ##4       #:7   <== 1.0e-4
     ##4       #:8   ==> -1.0e-4
      Absolute error = 2.0000000000e-4, Relative error = 2.0000000000e+0

     +++  File "many_columns1" differs from file "many_columns3"

does not show the same difference listing of the command 'numdiff -a
0.5:3-6 many_columns1 many_columns2'.

   If what you want is to obtain the same difference listing of 'numdiff
-a 0.5:3-6 many_columns1 many_columns2', then the right command is
'numdiff -X 2:2 -a 0.5:3-6:4-7 many_columns1 many_columns3'.  The report
printed by this last command is indeed
     ----------------
     ##1       #:2   <== 1
     ##1       #:3   ==> 1.1
      Absolute error = 1.0000000000e-1, Relative error = 1.0000000000e-1
     ##1       #:7   <== 1.0e-1
     ##1       #:8   ==> -1.0e-1
      Absolute error = 2.0000000000e-1, Relative error = 2.0000000000e+0
     ----------------
     ##2       #:2   <== 2
     ##2       #:3   ==> 2.2
      Absolute error = 2.0000000000e-1, Relative error = 1.0000000000e-1
     ##2       #:7   <== 1.0e-2
     ##2       #:8   ==> -1.0e-2
      Absolute error = 2.0000000000e-2, Relative error = 2.0000000000e+0
     ----------------
     ##3       #:2   <== 3
     ##3       #:3   ==> 3.3
      Absolute error = 3.0000000000e-1, Relative error = 1.0000000000e-1
     ##3       #:7   <== 1.0e-3
     ##3       #:8   ==> -1.0e-3
      Absolute error = 2.0000000000e-3, Relative error = 2.0000000000e+0
     ----------------
     ##4       #:2   <== 4
     ##4       #:3   ==> 4.4
      Absolute error = 4.0000000000e-1, Relative error = 1.0000000000e-1
     ##4       #:7   <== 1.0e-4
     ##4       #:8   ==> -1.0e-4
      Absolute error = 2.0000000000e-4, Relative error = 2.0000000000e+0

     +++  File "many_columns1" differs from file "many_columns3"

and up to the positions of the fields from 'many_columns3' coincides
with the one of 'numdiff -a 0.5:3-6 many_columns1 many_columns2'.

   The option '-a' can appear more times on the command line.  In case
of conflicts, the last setting is the one which matters.  If you look at
the report of the command 'numdiff -a 0.5:3-6 -a 0.08:4 many_columns1
many_columns2'
     ----------------
     ##1       #:2   <== 1
     ##1       #:2   ==> 1.1
      Absolute error = 1.0000000000e-1, Relative error = 1.0000000000e-1
     ##1       #:7   <== 1.0e-1
     ##1       #:7   ==> -1.0e-1
      Absolute error = 2.0000000000e-1, Relative error = 2.0000000000e+0
     ----------------
     ##2       #:2   <== 2
     ##2       #:2   ==> 2.2
      Absolute error = 2.0000000000e-1, Relative error = 1.0000000000e-1
     ##2       #:7   <== 1.0e-2
     ##2       #:7   ==> -1.0e-2
      Absolute error = 2.0000000000e-2, Relative error = 2.0000000000e+0
     ----------------
     ##3       #:2   <== 3
     ##3       #:2   ==> 3.3
      Absolute error = 3.0000000000e-1, Relative error = 1.0000000000e-1
     ##3       #:4   <== 9
     ##3       #:4   ==> 9.09
      Absolute error = 9.0000000000e-2, Relative error = 1.0000000000e-2
     ##3       #:7   <== 1.0e-3
     ##3       #:7   ==> -1.0e-3
      Absolute error = 2.0000000000e-3, Relative error = 2.0000000000e+0
     ----------------
     ##4       #:2   <== 4
     ##4       #:2   ==> 4.4
      Absolute error = 4.0000000000e-1, Relative error = 1.0000000000e-1
     ##4       #:4   <== 16
     ##4       #:4   ==> 16.16
      Absolute error = 1.6000000000e-1, Relative error = 1.0000000000e-2
     ##4       #:7   <== 1.0e-4
     ##4       #:7   ==> -1.0e-4
      Absolute error = 2.0000000000e-4, Relative error = 2.0000000000e+0

     +++  File "many_columns1" differs from file "many_columns2"

you see that 0.08 and not 0.5 is taken as threshold value for the
comparison of the fields in fourth position.

   Finally, if '-a' is not present on the command line, then the default
threshold value of zero applies to all comparisons of numerical fields
and any non null absolute difference is considered as significant,
unless some other option, for example '-P' or '-N', makes 'numdiff'
ignore it.

   The option '-r' can be used to make two numerical fields be
considered equal as long as their relative difference does not exceed a
certain threshold, which is specified by the argument that follows the
'-r' option.  As for the option '-a', the argument of '-r' can have
several forms.  These forms are the same accepted by '-a' and have the
same meanings, but the threshold value applies to the relative
difference, not to the absolute one.

   The relative difference is normally defined in this way.  If _n1_ is
a value from the file specified as first on the command line and _n2_ is
the corresponding value from the second file, then the absolute
difference is given by the formula _A=|n1-n2|_.  The relative difference
_R_ is given by:

   * _R = 0_ if _n1_ and _n2_ are equal,
   * _Inf_ (infinity) if _n2_ differs from _n1_ and at least one of them
     is zero,
   * _R = A/ min(|n1|, |n2|)_ if _n1_ and _n2_ are both non zero and
     _n2_ differs from _n1_.  _min(|n1|, |n2|)_ denotes the minimum
     between the absolute value of _n1_ and the absolute value of _n2_.

With this definition of relative difference it turns out that _R(n2, n1)
= R(n1, n2)_: the relative difference does not change if you only change
the ordering of the compared files on the command line.

   There are cases when this default definition of relative error makes
no sense.  This can happen for instance when one of the files is a
sample file containing a list of expected data, which could have been
computed theoretically or come from experiments in a laboratory.  In
this case it is more natural to define the relative difference as the
ratio between the absolute difference and the absolute value of the
number coming from the sample file.  If you use the option '-F' together
with the argument 1 (or 2), then Numdiff always compute the relative
difference as the ratio between the absolute difference and the absolute
value of the number from the first file (the second file, respectively).
More precisely, with '-F 1' the relative difference _R_ is computed
according to these rules:
   * _R = 0_ if _n1_ and _n2_ are equal,
   * _Inf_ (infinity) if _n2_ differs from _n1_ and _n1_ is zero,
   * _R = |n1-n2|/ |n1|_ if _n1_ is not zero and _n2_ differs from _n1_.

With '-F 2' the rules become:
   * _R = 0_ if _n1_ and _n2_ are equal,
   * _Inf_ (infinity) if _n2_ differs from _n1_ and _n2_ is zero,
   * _R = |n1-n2|/ |n2|_ if _n2_ is not zero and _n2_ differs from _n1_.

With the last two sets of rules it is not anymore true that _R(n2, n1) =
R(n1, n2)_: the relative difference changes, in the general case,
together with the ordering of the files on the command line.  As a
simple example, suppose that FILE1 and FILE2 contain
1    9.9  0.5  440

and
1.2  8    0.51 400

respectively.  Then 'numdiff FILE1 FILE2' displays
     ----------------
     ##1       #:1   <== 1
     ##1       #:1   ==> 1.2
      Absolute error = 2.0000000000e-1, Relative error = 2.0000000000e-1
     ##1       #:2   <== 9.9
     ##1       #:2   ==> 8
      Absolute error = 1.9000000000e+0, Relative error = 2.3750000000e-1
     ##1       #:3   <== 0.5
     ##1       #:3   ==> 0.51
      Absolute error = 1.0000000000e-2, Relative error = 2.0000000000e-2
     ##1       #:4   <== 440
     ##1       #:4   ==> 400
      Absolute error = 4.0000000000e+1, Relative error = 1.0000000000e-1

     +++  File "file1" differs from file "file2"

'numdiff -F 1 FILE1 FILE2' prints
     ----------------
     ##1       #:1   <== 1
     ##1       #:1   ==> 1.2
      Absolute error = 2.0000000000e-1, Relative error = 2.0000000000e-1
     ##1       #:2   <== 9.9
     ##1       #:2   ==> 8
      Absolute error = 1.9000000000e+0, Relative error = 1.9191919192e-1
     ##1       #:3   <== 0.5
     ##1       #:3   ==> 0.51
      Absolute error = 1.0000000000e-2, Relative error = 2.0000000000e-2
     ##1       #:4   <== 440
     ##1       #:4   ==> 400
      Absolute error = 4.0000000000e+1, Relative error = 9.0909090909e-2

     +++  File "file1" differs from file "file2"

the output of 'numdiff -F 2 FILE1 FILE2' is
     ----------------
     ##1       #:1   <== 1
     ##1       #:1   ==> 1.2
      Absolute error = 2.0000000000e-1, Relative error = 1.6666666667e-1
     ##1       #:2   <== 9.9
     ##1       #:2   ==> 8
      Absolute error = 1.9000000000e+0, Relative error = 2.3750000000e-1
     ##1       #:3   <== 0.5
     ##1       #:3   ==> 0.51
      Absolute error = 1.0000000000e-2, Relative error = 1.9607843137e-2
     ##1       #:4   <== 440
     ##1       #:4   ==> 400
      Absolute error = 4.0000000000e+1, Relative error = 1.0000000000e-1

     +++  File "file1" differs from file "file2"

'numdiff -F 1 -r 0.195 FILE1 FILE2' displays
     ----------------
     ##1       #:1   <== 1
     ##1       #:1   ==> 1.2
      Absolute error = 2.0000000000e-1, Relative error = 2.0000000000e-1

     +++  File "file1" differs from file "file2"

and finally, 'numdiff -F 2 -r 0.195 FILE1 FILE2' displays
     ----------------
     ##1       #:2   <== 9.9
     ##1       #:2   ==> 8
      Absolute error = 1.9000000000e+0, Relative error = 2.3750000000e-1

     +++  File "file1" differs from file "file2"

   The option '-2' is only meaningful when the user specifies a non-zero
tolerance threshold for both absolute and relative difference.  Without
this option 'numdiff' considers two numerical fields equal as long as at
least one between absolute and relative difference does not exceed the
corresponding threshold.  With the option '-2' 'numdiff' regards two
numerical fields as equal only if both absolute and relative difference
do not exceed the thresholds of tolerance specified for those fields.
For example, if FILE1 contains the unique line
100

and FILE2 the line
100.00012

then the output of the command 'numdiff FILE1 FILE2' will be

     ----------------
     ##1       #:1   <== 100
                     ==> 100.00012
     @ Absolute error = 1.2000000000e-4, Relative error = 1.2000000000e-6

     +++  File "FILE1" differs from file "FILE2"

The output of the commands 'numdiff -a 1.0e-4 FILE1 FILE2' and 'numdiff
-r 1.0e-6 FILE1 FILE2' will be the same as above, but 'numdiff -a 1.0e-4
-r 1.3e-6 FILE1 FILE2' and 'numdiff -a 1.3e-4 -r 1.0e-6 FILE1 FILE2'
will print the message

     +++  Files "FILE1" and "FILE2" are equal

since the relative difference is 1.2e-6 < 1.3e-6, the absolute
difference is 1.2e-4 < 1.3e-4, and it is sufficient that one of them
does not exceed its tolerance threshold.

   On the other hand, the commands 'numdiff -a 1.0e-4 -r 1.3e-6 -2 FILE1
FILE2' and 'numdiff -a 1.3e-4 -r 1.0e-6 -2 FILE1 FILE2' will both print
the message

     ----------------
     ##1       #:1   <== 100
                     ==> 100.00012
     @ Absolute error = 1.2000000000e-4, Relative error = 1.2000000000e-6

     +++  File "FILE1" differs from file "FILE2"

since the option '-2' makes 'numdiff' regard two values as equal only if
both absolute and relative difference do not exceed the respective
threshold of tolerance.

   The option '-P' makes 'numdiff' consider two values equal whenever
the second one, i.e.  the value coming from the file specified as last
on the command line, is less or equal than the first one, which is the
value coming from the file specified as first on the command line.  If
the values to compare are complex numbers, saying that the second one is
less or equal than the first one means that both real and imaginary part
of the second value are not greater than real and imaginary part of the
first value, respectively.

   Finally, the option '-N' makes 'numdiff' consider two values equal
whenever the second one, i.e.  the value coming from the file specified
as last on the command line, is greater or equal than the first one,
which is the value coming from the file specified as first on the
command line.  If the values to compare are complex numbers, saying that
the second one is greater or equal than the first one means that both
real and imaginary part of the second value are not less than real and
imaginary part of the first value, respectively.

   The options '-B', '-I', '-l', '-o', '-h', and '-v' do not require
further explanations.  The options '-l' and '-o' are only supplied for
the users of poorly designed operating systems, whose default shell does
not allow the redirection of standard error and standard output.  The
option '-I' has no effect on the outcome of numerical comparisons but
affects the action of the filter, *note Filtering::.

   The option '-s' requires as argument a set of characters, which will
be taken as field delimiters.  It is better to quote the set of the
delimiters, just as in the next examples:

     numdiff -s ' \t\n,;:.' FILE1 FILE2
     numdiff -s ' \t\n\r\f\v"\:;' FILE1 FILE2
     numdiff -s `` \t\n''' FILE1 FILE2

If you want to include in the set of delimiters also some special
characters, e.g.  the *blank*, then you must quote it.  I recommend you
to always use the single quote character (') to enclose the list of the
delimiters, since in this way you will prevent any substitution or
handling of characters by the shell.

'numdiff' recognizes and interprets the following sequences of
characters within the argument passed to the option '-s':

   * '\a' alert (bell),
   * '\b' backspace,
   * '\f' form feed,
   * '\n' newline,
   * '\r' carriage return,
   * '\s' blank,
   * '\t' horizontal tab,
   * '\v' vertical tab,
   * '\\' backslash,
   * '\NNN' the eight-bit character whose value is the octal value NNN
     (one to three digits),
   * '\xHH' the eight-bit character whose value is the hexadecimal value
     HH (one or two digits).

Thus, by passing the string ' \t\n,;:.' as argument for the option '-s'
one tells 'numdiff' to use as field delimiters the characters *blank*,
*horizontal tab*, *newline*, *comma*, *semicolon*, *colon*, and *dot*.
Passing ' \t\n' as argument to the option '-s' is the same as not using
at all the option '-s', since *blank*, *horizontal tab*, and *newline*
are the default field delimiters.

   In the list of field delimiters the character *backslash* ('\') is
always treated in a special way.  If it forms, combined with the
subsequent character(s), one of the escape sequences listed above, then
it is considered to be an escape character, and the whole escape
sequence is decoded as shown above.  Otherwise, the *backslash* is just
ignored.

   Therefore, the delimiters specified by the command line

     numdiff -s' \t\n\\\"' FILE1 FILE2

are *blank*, *horizontal tab*, *newline*, *backslash* and *double
quote*, since '\\' and '\"' are interpreted by 'numdiff' as '\' and '"'.

   Even if I have recommended to enclose the set of delimiters in single
quotes, there are cases in which you will be forced to use the double
quote character ('"') to enclose the set of field delimiters, e.g.  if
the single quote character is used itself as field delimiter, like in
one of the precedent examples.  However, you must take into account that
in this case the shell could make some substitutions on the command line
before executing 'numdiff'.  For instance, if your shell is GNU bash,
then (citing the man page of GNU bash)
     Enclosing characters in double quotes preserves the literal value
     of all characters within the quotes, with the exception of '$',
     '`', and '\'.  The characters '$' and '`' retain their special
     meaning within double quotes.  The backslash retains its special
     meaning only when followed by one of the following characters: '$',
     '`', '"', '\', or *<newline>*.  A double quote may be quoted within
     double quotes by preceding it with a backslash ...  The special
     parameters * and @ have special meaning when in double quotes ...

Therefore, if the set of delimiters is formed by ' ', '\t', '\n', '\'
and '"', and you decide to enclose them in double quotes, the 'numdiff'
command line should be

     numdiff -s'' \t\n\\\\\"'' FILE1 FILE2

and not

     numdiff -s'' \t\n\\\"'' FILE1 FILE2

In the latter case the shell would indeed replace the string

   ' \t\n\\\"'

by

   ' \t\n\"'

and then 'numdiff' would take ' ', '\t', '\n' and '"' as field
delimiters.

   'numdiff' requires the presence of the *newline* in the set of
characters passed to '-s'.  The absence of the *newline* in the set of
delimiters causes the issue of a warning message and the termination of
the program.

   If you run Numdiff with the option '-B' ('--binary') on files created
under MSDog/MSWindoze, then you should put the *carriage return* in the
set of field delimiters.  Otherwise, this character would be included in
all the fields which stay at the end of a line and this would cause some
undesirable effects.  For instance, a number put at the end of a line
would not be regarded as a numerical field by 'numdiff', since 'numdiff'
would consider the final *carriage return* as part of the field, and
this one would be then qualified as non-numerical.

   You can specify different delimiters for the two files to compare by
putting the prefix '1:' or '2:' in front of the set of characters passed
to '-s'.  If the argument of '-s' begins with '1:', the characters after
this prefix are used as field delimiters only for the file passed as
first on the command line.  Analogously, if the prefix is '2:', then the
characters after it are used as field delimiters only for the file
specified as second on the command line.  You can also provide an
explicit set of delimiters for just one of the files to compare, in
which case 'numdiff' uses the default field delimiters *blank*, *tab*
and *newline* for the other file.  Therefore, with 'numdiff -s '1:: \n'
FILE1 FILE2' the program will take *colon*, *blank* and *newline* as
delimiters for FILE1, and *blank*, *tab* and *newline* as delimiters for
FILE2.  The recommendations about quoting the set of delimiters are
valid also in presence of a prefix.

   Starting from version 5.8 'numdiff' allows to specify whole strings
as field delimiters instead of single characters.  To this purpose the
option '-D' is provided.  Assume that file 'register1' and file
'register2' contain
--A:    +1.0---
--B:    -2.0---
--C:    +3.0---
--D:    -4.0---
--E:    +5.0---
--F:    -6.0---

and
--a:    +1.1---
--b:    -2.2---
--c:    +3.3---
--d:    -4.4---
--e:    +5.5---
--f:    -6.6---

respectively.  Assume in addition, you would like that the dashes at the
begin and at the end of every line are treated as delimiters and then
neglected during the line by line comparison.  To obtain this you cannot
just specify the character - (minus) as delimiter via the option '-s':
if you do it, the negative numbers appearing in the two files will be
treated as positive, since the minus sign will be regarded as a
delimiter.  By means of the option '-D' you can tell 'numdiff' to
consider the strings -- and --- as field delimiters, but not the single
character -.  To see this in practice, look at the output of the command
'numdiff -D ': -- --- \s \n' register1 register2':
     ----------------
     ##1       #:1   <== A
     ##1       #:1   ==> a
                                                          @
     ##1       #:2   <== +1.0
     ##1       #:2   ==> +1.1
      Absolute error = 1.0000000000e-1, Relative error = 1.0000000000e-1
     ----------------
     ##2       #:1   <== B
     ##2       #:1   ==> b
                                                          @
     ##2       #:2   <== -2.0
     ##2       #:2   ==> -2.2
      Absolute error = 2.0000000000e-1, Relative error = 1.0000000000e-1
     ----------------
     ##3       #:1   <== C
     ##3       #:1   ==> c
                                                          @
     ##3       #:2   <== +3.0
     ##3       #:2   ==> +3.3
      Absolute error = 3.0000000000e-1, Relative error = 1.0000000000e-1
     ----------------
     ##4       #:1   <== D
     ##4       #:1   ==> d
                                                          @
     ##4       #:2   <== -4.0
     ##4       #:2   ==> -4.4
      Absolute error = 4.0000000000e-1, Relative error = 1.0000000000e-1
     ----------------
     ##5       #:1   <== E
     ##5       #:1   ==> e
                                                          @
     ##5       #:2   <== +5.0
     ##5       #:2   ==> +5.5
      Absolute error = 5.0000000000e-1, Relative error = 1.0000000000e-1
     ----------------
     ##6       #:1   <== F
     ##6       #:1   ==> f
                                                          @
     ##6       #:2   <== -6.0
     ##6       #:2   ==> -6.6
      Absolute error = 6.0000000000e-1, Relative error = 1.0000000000e-1

     +++  File "register1" differs from file "register2"

The argument '-D ': -- --- \s \n'' instructs 'numdiff' to regard every
occurrence of a colon (:), of a blank (\s), of a newline (\n), as well
as every occurrence of the strings -- and --- as field delimiters.  The
minus sign in front of the negative numbers is then properly handled.

   In general the argument to the option '-D' is a blank separated
sequence of one or more strings each of which contains no blank.  Thus,
the general form of the argument to the option '-D' is
     STRING1 STRING2 ... STRINGN

where STRING1, STRING2, and so on are sequences of one or more
characters (strings) containing no blank.

   Mind that at least one of these strings must be '\n'.  In addition,
if a string contains the newline character, this must be the only one:
strings like '#\n', '%%\n', or '\s\n' are not allowed (entering such a
string makes the program terminate after issuing a warning message).

   Since the blank character has a special meaning for the shell, if the
argument of '-D' is formed by two or more strings it should be quoted
either with a single (''') or with a double quote ('"').  Quoting is
also adviced if one of the strings passed to '-D' contains a character
(or a sequence of characters) having a special meaning for the shell.

   For the usage of single and double quoting to delimit the argument of
'-D' the same warnings and recommendations apply as for the argument of
'-s'.

   If you want to set as delimiter a string which contains one or more
blanks, then you have to make use of the escape sequence '\s', like in
the example above: within the argument of '-D' the blank character is
always interpreted as a separator of adjacent delimiters.

   More generally, when writing the argument of '-D' the same escape
sequences are allowed as for the argument of '-s'.  This turns out to be
particularly useful whenever a multibyte character is used as delimiter
in (one of) the files to compare.  As example consider the comparison
between 'ledger1':
                  In                            Out

     Jan      1200.00Euro                1000.00Euro
     Feb       800.40Euro                 650.00Euro
     Mar      1620.50Euro                1500.00Euro
     Apr       760.00Euro                 900.00Euro

     Total    4380.90Euro                4050.00Euro

     Difference: +330.90Euro

and 'ledger2':
                  In                            Out

     Jan      1100.00Euro                1000.00Euro
     Feb       800.40Euro                 750.00Euro
     Mar      1620.50Euro                1700.00Euro
     Apr       750.00Euro                 900.00Euro

     Total    4270.90Euro                4350.00Euro

     Difference: -79.10Euro

   Since the Euro symbol is attached to all values, 'numdiff' cannot
compare them in the proper way if it is run with the default field
delimiters, as the output of the command 'numdiff ledger1 ledger2'
shows:
     ----------------
     ##3       #:2   <== 1200.00Euro
     ##3       #:2   ==> 1100.00Euro
                                                          @
     ----------------
     ##4       #:3   <== 650.00Euro
     ##4       #:3   ==> 750.00Euro
                                                          @
     ----------------
     ##5       #:3   <== 1500.00Euro
     ##5       #:3   ==> 1700.00Euro
                                                          @
     ----------------
     ##6       #:2   <== 760.00Euro
     ##6       #:2   ==> 750.00Euro
                                                          @
     ----------------
     ##8       #:2   <== 4380.90Euro
     ##8       #:2   ==> 4270.90Euro
                                                          @
     ##8       #:3   <== 4050.00Euro
     ##8       #:3   ==> 4350.00Euro
                                                          @
     ----------------
     ##10      #:2   <== +330.90Euro
     ##10      #:2   ==> -79.10Euro
                                                          @

     +++  File "ledger1" differs from file "ledger2"

The trick to perform the comparison in the proper way consists in
specifying the Euro symbol as field delimiter, in addition to blank,
horizontal tabulation and newline.  If 'ledger1' and 'ledger2' are
encoded in UTF-8, this can be done by using the option '-D' with the
argument '\xE2\x82\xAC \s \t \n', since the hexadecimal representation
of Euro in UTF8 is given by the byte sequence 0xE2 0x82 0xAC. On my PC
the output of the command 'numdiff -D '\xE2\x82\xAC \s \t \n' ledger1
ledger2' shows that with such a choice of the delimiters 'numdiff'
performs indeed a numerical comparison of the values contained in the
two files:
     ----------------
     ##3       #:2   <== 1200.00
     ##3       #:2   ==> 1100.00
      Absolute error = 1.0000000000e+2, Relative error = 9.0909090909e-2
     ----------------
     ##4       #:3   <== 650.00
     ##4       #:3   ==> 750.00
      Absolute error = 1.0000000000e+2, Relative error = 1.5384615385e-1
     ----------------
     ##5       #:3   <== 1500.00
     ##5       #:3   ==> 1700.00
      Absolute error = 2.0000000000e+2, Relative error = 1.3333333333e-1
     ----------------
     ##6       #:2   <== 760.00
     ##6       #:2   ==> 750.00
      Absolute error = 1.0000000000e+1, Relative error = 1.3333333333e-2
     ----------------
     ##8       #:2   <== 4380.90
     ##8       #:2   ==> 4270.90
      Absolute error = 1.1000000000e+2, Relative error = 2.5755695521e-2
     ##8       #:3   <== 4050.00
     ##8       #:3   ==> 4350.00
      Absolute error = 3.0000000000e+2, Relative error = 7.4074074074e-2
     ----------------
     ##10      #:2   <== +330.90
     ##10      #:2   ==> -79.10
      Absolute error = 4.1000000000e+2, Relative error = 5.1833122630e+0

     +++  File "ledger1" differs from file "ledger2"

   If 'ledger1' and 'ledger2' had been saved using a multi-byte encoding
different from UTF-8, then the sequence of bytes which corresponds to
Euro in this other encoding should have been passed to '-D'.

   As for '-s', with '-D' you can specify different delimiters for the
two files to compare by means of the prefixes '1:' and '2:', like in
'numdiff -D '1:\t \n' -D '2: -- \s \n' first_file second_file'.  The
recommendations about quoting the set of delimiters are valid also in
presence of a prefix.  Mind that, if you provide an explicit set of
delimiters for just one of the files to compare, 'numdiff' uses the
default field delimiters *blank*, *tab* and *newline* for the other
file.

   If you run Numdiff with the option '-B' ('--binary') on files created
under MSDog/MSWindoze, you should always include the character '\r' in
the set of field delimiters.

   The option '-s' and '-D' can appear more than once on the command
line.  In case of conflicts, 'numdiff' assumes as set of delimiters for
a given file the one specified last on the command line.

   By means of the option '-#' the user can set the number of digits in
the significands used in multiple precision arithmetic.  The default
value is 35, the largest admissible value is 180.  If 'numdiff' has been
linked against the GNU Multiple Precision Arithmetic Library (also
called GNU MP), then the precision it uses is typically higher than the
specified one.  On my machine the actual value of the precision is 20 if
the user requests a value between 0 and 20, 30 if the user specifies a
precision between 21 and 30, 40 for a user-specified value between 31
and 40, and so on.  Anyway, the actual precision is never less than the
one requested by the user.

Take into account that an higher precision makes the execution of
'numdiff' slower.  This is particularly true if 'numdiff' is not using
the computational routines from the GNU MP library and the files to
compare contain a lot of numerical fields.  In addition, mind that
'numdiff' truncates the value of a numerical field if it has too much
digits with respect to the current precision.  To be precise, denoted by
P the current value of the precision, the following rules apply.
   * If 'numdiff' has been built with its own internal support for
     multiple precision arithmetic, then
        * if a number is written in ordinary decimal notation, 'numdiff'
          will consider, in addition to all digits of the integer part,
          only the first P digits of the fractional part;
        * if a value is written in scientific notation, then 'numdiff'
          will only consider the first P digits of the fractional part
          of the mantissa.
   * If 'numdiff' uses the routines from the GNU MP library to perform
     its computations, the value of a numerical field is first
     translated into scientific notation and then only the first P
     digits of the fractional part of the mantissa are considered.

You can find out whether your local version of 'numdiff' is relying on
GNU MP or not by executing the command 'numdiff -v'.  If 'numdiff' uses
GNU MP, then this command will display the following message or similar
(possibly translated into your mother language) among other information:
     The software has been linked against
     the GNU Multiple Precision Arithmetic Library,
     version number 4.2.4.

If 'numdiff' does not rely on GNU MP, then the displayed message will be
(up to translation into your mother language)
     The software has been built with
     its own internal support for multiple precision arithmetic.

By means of the option '-c' the user can qualify a string as a symbol or
name for a currency.  The string passed as argument to this option is
ignored whenever it appears immediately before the first digit of a
number.  In particular, the presence of this string does not prevent a
field from being considered of numeric type.  By prefixing the argument
of '-c' with '1:' or '2:' it is possible to set the currency name/symbol
only for one of the compared files, or to specify different currency
names for the two files.  As example we consider the files 'money1':
	Profits			Expenses

	+$430.10		-$300.50
	+$750.20		-$550.02
	+$876.24		-$720.00

Totals  $2056.54               -$1570.52

and 'money2':
	Profits			Expenses

	USD430.10		-USD300.50
	USD750.20		-USD550.02
	USD876.24		-USD720.15

Totals    2056.54                 -1570.67
   To properly compare them, we have to tell 'numdiff' that '$' and
'USD' are the currency symbols for 'money1' and 'money2', respectively.
This can be achieved by '-c 1:$' and '-c 2:USD'.  The output of the
command 'numdiff -c 1:$ -c 2:USD money1 money2' is
     ----------------
     ##5       #:2   <== -$720.00
     ##5       #:2   ==> -USD720.15
      Absolute error = 1.5000000000e-1, Relative error = 2.0833333333e-4
     ----------------
     ##7       #:3   <== -$1570.52
     ##7       #:3   ==> -1570.67
      Absolute error = 1.5000000000e-1, Relative error = 9.5509767466e-5

     +++  File "money1" differs from file "money2"

as it is reasonable to expect.

   The argument of '-c' may also be a multi-byte string, in particular a
multi-byte string encoded in UTF-8.  If your locale uses UTF-8 as
encoding, you can write the argument directly in this form.  For
instance, you can write '-c Euro' to specify as currency name the Euro
symbol.  If your locale does not use UTF-8 as encoding, or UTF-8 is not
supported by your terminal, you may still write an UTF-8 encoded string
as a multi-byte string by specifying each single byte of every
(multi-byte) character.  To this purpose you can use the same octal and
hexadecimal escape sequences recognized by the options '-s' and '-D',
but then the argument of '-c' has to be quoted to avoid the
interpretation of the hexadecimal escape sequences by the shell.

   For example, if the files to compare are encoded in UTF-8, you can
set Euro as currency name by adding '-c '\xE2\x82\xAC'' to the command
line of 'numdiff', since the hexadecimal representation of Euro in UTF-8
is given by the sequence of bytes 0xE2 0x82 0xAC.

   To see this in practice, if 'euro1' contains the text
     	Profits			       Expenses

     	+Euro430.10		      -Euro300.50
     	+Euro750.20		      -Euro550.02
     	+Euro876.24		      -Euro720.00

and 'euro2' the text
     	Profits			       Expenses

     	+Euro430.10		      -Euro300.00
     	+Euro750.20		      -Euro550.02
     	+Euro876.00		      -Euro720.00

then the report of 'numdiff -c '\xE2\x82\xAC' euro1 euro2' is
     ----------------
     ##3       #:2   <== -Euro300.50
     ##3       #:2   ==> -Euro300.00
      Absolute error = 5.0000000000e-1, Relative error = 1.6666666667e-3
     ----------------
     ##5       #:1   <== +Euro876.24
     ##5       #:1   ==> +Euro876.00
      Absolute error = 2.4000000000e-1, Relative error = 2.7397260274e-4

     +++  File "euro1" differs from file "euro2"

   Please consider that '-c' is only provided to let 'numdiff' regard a
field as numeric also in presence of a currency name immediately before
its first digit: 'numdiff' does not know anything about currencies and
can not perform any kind of conversion between them.  In addition, mind
that the number after the currency name can be written in any format,
not only in financial notation.  'numdiff' can even cope with the
currency name when it appears in a complex number.  For example, with
'-c EUR' 'numdiff' considers +EUR12-EUR0.24i and +12-0.24i as equal.

   The options '-d', '-t', '-g', '-p', '-n', '-e' and '-i' can be used
to instruct 'numdiff' about the numeric formats used in the files which
it is going to compare.  Since the two files to compare do not have to
adopt the same numeric format, 'numdiff' allows to specify different
numeric formats for them.  Each of the options '-d', '-t', '-g', '-p',
'-n', '-e', and '-i' can have as argument one or two (single-byte)
characters, in particular one or two digits if the option is '-g'.  In
the first case the argument refers to both files to compare, in the
second case the first character is for the file specified first on the
command line, the second character for the file specified last.  For
instance, the option '-d' can be used to tell 'numdiff' which
character(s) is(are) used to indicate the decimal point in the two files
to compare.  If you give the command 'numdiff -d_ FILE1 FILE2', then
'numdiff' will understand that both in FILE1 and in FILE2 the character
*underscore* ('_') is used in place of the default one ('.') to indicate
the position of the decimal point in the numerical values.  But if the
command is 'numdiff -d_: FILE1 FILE2', then 'numdiff' will understand
that the decimal point is indicated by the character *underscore* in
FILE1, and by *colon* (':') in FILE2.

   If you omit to use one of the options '-d', '-t', '-g', '-p', '-n',
'-e', and '-i', then the corresponding attribute will take its default
value, *note Default Numeric Format::.

   You should be careful whenever you use one or more of these options.
First, not all characters can be passed to them as arguments.  The
arguments of the option '-g' must be digits, the arguments of the
options '-d' and '-t' must be punctuation marks (punctuation marks are
all the characters of the ASCII set for which the standard C function
'ispunct' returns a non zero value), those ones of the options '-p',
'-n', '-e' and '-i' must be graphical characters but digits (graphical
characters are all the characters of the ASCII set for which the
standard C function 'isgraph' returns a non zero value).

   It is not possible to set the decimal point, the thousands separator,
the positive sign, the negative sign, the prefix for decimal exponent or
the symbol of the imaginary unit in such a way that, for a same file,
two or more of these characters come out to be equal.  This rule also
applies if you miss/omit to explicitly select a symbol through the
appropriate option.  For instance, the command 'numdiff -d,. FILE1
FILE2' will make 'numdiff' abnormally terminate after printing the error
message:

     The numeric format specified for the first file is illegal,
     the following symbols should be all different
     while two or more of them are actually equal:

     Decimal point = `,'
     Thousands separator = `,'
     Leading positive sign = `+'
     Leading negative sign = `-'
     Prefix for decimal exponent = `e'
     Symbol used to denote the imaginary unit = `i'

With the option '-d' we have told 'numdiff' that in the first file the
decimal point is indicated by the character *comma*, but at the same
time we have not modified the character in use to separate the groups of
thousands, which has remained the default one, i.e.  *comma*, for both
files to compare.  In this way we have implicitly told that in FILE1 the
character *comma* represents both decimal point and thousands separator.
Since this is not reasonable, 'numdiff' refuses to work.  To avoid this
problem it would be sufficient to set explicitly the thousands separator
by means of the option '-t': 'numdiff -d,. -t., FILE1 FILE2'.  Of
course, we assume here that the decimal point and the thousands
separator are represented in FILE1 by *comma* and *dot* respectively, in
FILE2 by *dot* and *comma*.

   I strongly suggest you, whenever you write a file, to avoid using the
same symbol for two different things (like would be using *comma* for
both decimal point and thousands separator), it is nonsense.

   At last, it is possible (but silly) to specify as argument for the
options '-d', '-t', '-g', '-p', '-n', '-e', or '-i' one of the
characters used as delimiters in the files to compare.  'numdiff' does
not complain, but you have to consider that the program first uses the
set of field delimiters to split the files into fields and only
afterwards, when it has to distinguish between numerical and
non-numerical fields, it takes into account the numeric formats
specified for the two files.  To prevent conflicts, you should then
avoid to specify as argument for the options '-d', '-t', '-g', '-p',
'-n', '-e', or '-i' a character which is also used as field delimiter.
As a general rule, in writing a file you should avoid using the same
symbol to mean two different things.  What we have said also explains
why the argument of the option '-c' should never contain field
delimiters.

   The option '-X' can be used to restrict the comparison between files
to a certain group of fields.  This option requires as argument a range
of positive integer values or eventually just one positive integer
number.  The argument indicates the position(s) of the fields that
'numdiff' has to ignore.  Remember that the fields of a line are
numerated starting from the left hand of the line and proceeding towards
the right hand.

   The argument passed to '-X' can start with a prefix, which must be
either '1:' or '2:'.  '1:' refers to the file passed as first on the
command line, '2:' to the file specified as second.  With the prefix
'1:' only the fields of the first file corresponding to the specified
position(s) are ignored.  Similarly, you have to use the prefix '2:' if
you want to ignore only fields from the second file.

   The option '-X' can appear more times on the command line, in which
case 'numdiff' will ignore all fields located in the positions so
specified.  Some examples can clarify the use of ranges and prefixes.
If the file 'List1' contains the data
* a  1    1     1     1
* b  2    2     2     2
* c  3    3     3     3
* d  4    4     4     4
* e  5    5     5     5

and 'List2' the data
     1    1.1  1.01   A  1.001  1.0001
     2    2.2  2.02   B  2.002  2.0002
     3    3.3  3.03   C  3.003  3.0003
     4    4.4  4.04   D  4.004  4.0004
     5    5.5  5.05   E  5.005  5.0005

then the output of 'numdiff -X 1:1-2 -X 2:4 -X 1:6 -X 2:5-6 List1 List2'
is
     ----------------
     ##1       #:4   <== 1
     ##1       #:2   ==> 1.1
     @ Absolute error = 1.0000000000e-1, Relative error = 1.0000000000e-1
     ##1       #:5   <== 1
     ##1       #:3   ==> 1.01
     @ Absolute error = 1.0000000000e-2, Relative error = 1.0000000000e-2
     ----------------
     ##2       #:4   <== 2
     ##2       #:2   ==> 2.2
     @ Absolute error = 2.0000000000e-1, Relative error = 1.0000000000e-1
     ##2       #:5   <== 2
     ##2       #:3   ==> 2.02
     @ Absolute error = 2.0000000000e-2, Relative error = 1.0000000000e-2
     ----------------
     ##3       #:4   <== 3
     ##3       #:2   ==> 3.3
     @ Absolute error = 3.0000000000e-1, Relative error = 1.0000000000e-1
     ##3       #:5   <== 3
     ##3       #:3   ==> 3.03
     @ Absolute error = 3.0000000000e-2, Relative error = 1.0000000000e-2
     ----------------
     ##4       #:4   <== 4
     ##4       #:2   ==> 4.4
     @ Absolute error = 4.0000000000e-1, Relative error = 1.0000000000e-1
     ##4       #:5   <== 4
     ##4       #:3   ==> 4.04
     @ Absolute error = 4.0000000000e-2, Relative error = 1.0000000000e-2
     ----------------
     ##5       #:4   <== 5
     ##5       #:2   ==> 5.5
     @ Absolute error = 5.0000000000e-1, Relative error = 1.0000000000e-1
     ##5       #:5   <== 5
     ##5       #:3   ==> 5.05
     @ Absolute error = 5.0000000000e-2, Relative error = 1.0000000000e-2

     +++  File "List1" differs from file "List2"

Numdiff cuts off from 'List1' the fields in the positions 1, 2 and 6 and
from 'List2' the fields in the positions 4, 5 and 6.  In this way it
compares the third, fourth and fifth field of every line of 'List1' with
the first, second and third field respectively of the corresponding line
of 'List2'.  An equivalent form of the command 'numdiff -X 1:1-2 -X 2:4
-X 1:6 -X 2:5-6 List1 List2' is given by 'numdiff -X 1:1-2 -X 2:4-5 -X 6
List1 List2' : since the sixth field is cut off from both files, we can
refer to it without a prefix.

   As you can see, you can specify a range of fields by using the
notation 'M-N', where M and N are the field numbers of the first and of
the last field in the range.  It is even possible to use range
expressions like 'M-' or '-N'.  The first expression corresponds to all
fields starting from the Mth one (inclusive) till to the end of line,
the second selects all fields from the first one till to the Nth one
(inclusive).  Therefore the command 'numdiff -X 1:1-2 -X 2:4 -X 1:6 -X
2:5-6 List1 List2' is equivalent to 'numdiff -X 1:-2 -X 2:4 -X 1:6 -X
2:5- List1 List2' and to 'numdiff -X 1:-2 -X 1:6 -X 2:4- List1 List2'.

   Mind that, while writing a specification for the option '-X', the
largest field number you can use is 32768.

   If you employ the option '-X' the exit status of 'numdiff' reflects
the outcome of the restricted comparison.  For instance, the exit status
of 'numdiff -X 8- FILE1 FILE2' is 1 only if 'numdiff' has found a
difference in the first seven fields of FILE1 and FILE2.  If the two
files differ only in the fields after the seventh one, then 'numdiff'
ends with a zero exit status.

   Going back to the example with 'List1' and 'List2', the output of
'numdiff -X 1:1-2 -X 1:4- -X 2:2- List1 List2' is

     +++  Files "List1" and "List2" are equal

since every field of 'List1' at position 3 is equal to the first field
in the corresponding line of 'List2'.  The exit code returned by the
program to the shell is in this case zero.

   The options '-z', '-Z', '-m', '-H', '-f', and '-T' influence the
action of the filter and their use is then described later, *note
Filtering::.  Care that '-z' and '-Z' need both an argument in the same
form required by '-X'.

   Since version 5 Numdiff accepts also long options to conform to the
GNU standards.  For example, now it is possible to use
'--separators='\n\t %'' or '--separators '\n\t %'' instead of using '-s
'\n\t %''.

   The long options, which start all with two dashes, are listed at the
beginning of this chapter, each one near to the corresponding short
option.

   The argument of a long option may or may not be preceded by the =
sign.  The only exceptions are the options '--test-filter' and
'--overview', for which the presence of the = before the argument is
mandatory.  Thus, '--test-filter=60' is correct while '--test-filter 60'
is not accepted.

   ---------- Footnotes ----------

   (1) By major numerical differences and major errors I mean those ones
listed in the output of 'numdiff' if none of the options '-U', '-f',
'-O', and '-q' is used.

6 Selecting lines and fields for the comparison
***********************************************

Together with the version 5.x of Numdiff is shipped the program
'ndselect'.  Originally, I decided to create this utility in order to
deal with a situation that comes out often in Numerical Analysis.  Here
I present a very simple example of such a situation.  Let us suppose
that file 'list1' contains the values of the square root, rounded to the
20th decimal digit, for all integer numbers between 12 and 24:
12       3.46410161513775458705
13       3.60555127546398929312
14       3.74165738677394138558
15       3.87298334620741688518
16       4
17       4.12310562561766054982
18       4.24264068711928514641
19       4.35889894354067355224
20       4.47213595499957939282
21       4.58257569495584000659
22       4.69041575982342955457
23       4.7958315233127195416
24       4.89897948556635619639

File LIST2 contains _suitable_ approximations of the square root only
for the numbers between 12 and 21 which are multiple of 3:

12       3.46410162002945508100
15       3.87298387096774193548
18       4.24264705882352941176
21       4.58260869565217391304

These approximations could have been obtained by using the famous
Heron's algorithm: given an approximation 'a' for the square root of a
number 'x', a better approximation is computed by using the formula 'a
:= 0.5 * (x/a + a)'.  What we want now is to understand by means of
'numdiff' how good the approximations contained in file LIST2 are.
Unfortunately, we cannot execute directly the command 'numdiff list1
list2', since in this way we would compare the approximations provided
for the square roots of 15, 18, and 21 with the square roots of 13, 14,
and 15, respectively.  To make the comparison in the right way, one
could open 'list1' in a text editor and remove from this file all lines
but the ones related to the numbers 12, 15, 18, and 21.  This approach
is practicable since we have to remove only a few lines: one can easily
figure out how boring and inefficient would be to manually remove
hundreds or thousands of lines from a file.

   An expert GNU user would suggest that it is possible to automate this
removal by using the well known utilities 'head' and 'sed', in this
particular case 'head -n 10 list1 | sed -n -e '1~3 p' > List1'.  A quick
explanation for the ones who do not know how to use 'head' and 'sed':
the previous command extracts from 'list1' the first 10 lines, namely
the lines containing the square roots of the numbers from 12 to 21, then
picks every third line starting from the first one to select only the
lines related to 12, 15, 18, and 21.  Finally, these lines are printed
to the file 'List1', which then looks like:
12       3.46410161513775458705
15       3.87298334620741688518
18       4.24264068711928514641
21       4.58257569495584000659

   Once obtained 'List1', we can perform the comparison between the
values we are interested in by means of 'numdiff List1 list2' .
Unfortunately, this trick only works if you have installed the GNU
version of 'sed' which, as far as I know, is the only one providing the
extension FIRST~STEP to specify line addresses.  This is why I decided
to implement 'ndselect', which allows to obtain the same result as above
with the simpler command 'ndselect -b 1 -e 10 -s 3 list1 > List1'.

   The meaning of the arguments passed to the options '-b', '-e', and
'-s' is the following: we tell 'ndselect' to print every third line of
file 'list1' (the option '-s' specifies the step) starting from the
first one (the option '-b' specifies the beginning) and ending within
the tenth one possibly inclusive (the option '-e' specifies the end).
Because of the presence of the redirection operator '>', the previous
command sends to the file 'List1' what 'ndselect' would print to the
screen (standard output).

   Since version 5.6 'ndselect' can also be used to select particular
fields of a file.  Instead of printing all fields of every line, you may
want to print indeed only the fields at particular positions.  To do
this you can employ the option '-F' to indicate the position of the
first field to print, the option '-L' to indicate the position of the
last field that can be printed, the option '-I' to set the increment
when selecting the fields.  In addition, the option '-S' can be used to
specify a set of field delimiters different from the default one (which
consists of *blank*, *tab* and *newline*).  As for 'numdiff', the field
delimiters are used to split the input lines into fields.

   The option '-S' of 'ndselect' recognizes and accepts the same escape
sequences of 'numdiff' options '-s', '-D', and '-c'.

   As example consider the selection of the even fields between the
second and the sixth one inclusive from the file 'many_many_columns',
whose contents are shown here:
A |   I | 1.1 |   1.08  |   1.01  |  0.1  |   11.011    |    -1.0e-1
B |  II | 2.2 |   2.16  |   4.04  |  0.4  |   24.024    |    -1.0e-2
C | III | 3.3 |   3.24  |   9.09  |  0.9  |   39.039    |    -1.0e-3
D |  IV | 4.4 |   4.32  |  16.16  |  1.6  |  416.039    |    -1.0e-4
E |   V | 5.5 |   5.40  |  25.25  |  2.5  |  525.416    |    -1.0e-5
F |   # |  #  |    #    |    #    |   #   |     #       |      #

This selection can be accomplished by means of the command 'ndselect -S
'| \t\n' -F 2 -L 6 -I 2 many_many_columns', whose output shows only the
selected fields:
     I | 1.08  |   0.1
     II | 2.16  |   0.4
     III | 3.24  |   0.9
     IV | 4.32  |  1.6
     V | 5.40  |  2.5
     # |  #    |    #

Of course, you can also select particular fields of particular lines, as
shown by the output of the command 'ndselect -S '| \t\n' -b 1 -e 5 -s 3
-F 2 -L 6 -I 2 many_many_columns':
     I | 1.08  |   0.1
     IV | 4.32  |  1.6

   By default, 'ndselect' reuses the delimiters found in the input lines
while writing the selected fields to the standard output.  You can
specify a custom separator by means of the option '-O'.  This one
recognizes and accepts the same escape sequences of 'numdiff' options
'-s', '-D', and '-c'.  For example, 'ndselect -S '| \t\n' -b 1 -e 5 -s 3
-F 2 -L 6 -I 2 -O '\t\t' many_many_columns' puts two horizontal
tabulations after every printed field:
I		1.08		0.1
IV		4.32		1.6

   Even if the implementation of a filter in 'numdiff' and the addition
of the option '-X' have made 'ndselect' much less useful than in the
past, this tool can still be used to handle some special cases.  In
addition, it can be used as a filter for other programs than 'numdiff'.
The complete synopsis of 'ndselect' can be found in the next chapter.

7 Invoking ndselect
*******************

*SYNOPSIS*

        ndselect -h|--help|-v|--version
   or
        ndselect [-b N][-e N][-s N][-F N][-L N][-I N][-S IFS][-D DELIMS]
        [-O OSEP][-x][-l PATH][-o PATH][FILE]

where FILE is the name of the file to read from.

   In the first case 'ndselect' prints a short help or/and version
number, Copyright, License notice, and NO-Warranty disclaimer.  In the
second case 'ndselect' prints to the standard output a subset of lines
and fields from FILE.  The complete path of FILE should be given, a
directory name is not accepted.  If no input file is specified, the
program reads from the standard input.

*OPTIONS*

'-b, --beginning, --start=N'
     Set to N the number of the first line to print (The default
     behavior is to start with line number 1)

'-e, --end=N'
     Set to N the number of the last line that can be printed (The
     default behavior is to arrive till to the end of the file)

'-s, --step=N'
     Set to N the increment to use when selecting the lines to print
     (The default value for the increment is 1)

'-F, --first-field=N'
     Set to N the number of the first field to print (The default
     behavior is to start with field number 1)

'-L, --last-field=N'
     Set to N the number of the last field that can be printed (The
     default behavior is to arrive till to the end of every line)

'-I, --increment=N'
     Set to N the increment to use when selecting the fields to print
     (The default value for the increment is 1)

'-S, --separators=IFS'
     Specify the set of characters to use as delimiters while splitting
     the input lines into fields (The default set of delimiters is
     space, tab and newline)

'-D, --delimiters=DELIMS'
     Specify the set of strings to use as delimiters while splitting the
     input lines into fields (The default set of delimiters is space,
     tab and newline)

'-O, --output-separator=OSEP'
     Specify the string to use as separator while writing the selected
     fields to the standard output (The default behavior consists in
     reusing the delimiters found in the input lines)

'-x, --omit-empty-lines'
     Do not print empty lines

'-l, --warnings-to=PATH'
     Redirect warning and error messages from stderr to the indicated
     file

'-o, --output=PATH'
     Redirect output from stdout to the indicated file

'-h, --help'
     Show this help message

'-v, --version'
     Show version number, Copyright, Distribution Terms and NO-Warranty

Passing 0 as argument to the option '-L' or to '-e' is equivalent to
omit this option and leave enabled the default behavior (which consists
in scanning till to the end of the line and of the file, respectively).

*DIAGNOSTICS*

   The exit status is 0 in case of normal termination, -1 (255) in case
of error.

As 'numdiff' does, since version 5 also 'ndselect' accepts long options.
Thus, instead of 'ndselect -b 1 -e 10 -s 3 list1 > List1' you can write
'ndselect --start=1 --end=10 --step=3 list1 > List1'.

   The usage of the option '-D' is the same as for 'numdiff'.  The
option '-S' corresponds to the option '-s' of 'numdiff'.

8 Using the filter of numdiff
*****************************

Since version 5 you can activate a filter when launching 'numdiff' to
make the program appropriately compare the given files even if they do
not have the same structure.  Recalling the example of chapter 6, if you
run the command 'numdiff -z 2- -V list1 list2' you obtain the following
result:

     ----------------
     ##1       <== 12       3.46410161513775458705
     ##1       ==> 12       3.46410162002945508100

     ##1       #:2   <== 3.46410161513775458705
     ##1       #:2   ==> 3.46410162002945508100
      Absolute error = 4.8917004940e-9, Relative error = 1.4121122985e-9
     ----------------
     ##2       <== 13       3.60555127546398929312
               ==>

     ----------------
     ##3       <== 14       3.74165738677394138558
               ==>

     ----------------
     ##4       <== 15       3.87298334620741688518
     ##2       ==> 15       3.87298387096774193548

     ##4       #:2   <== 3.87298334620741688518
     ##2       #:2   ==> 3.87298387096774193548
      Absolute error = 5.2476032505e-7, Relative error = 1.3549253331e-7
     ----------------
     ##5       <== 16       4
               ==>

     ----------------
     ##6       <== 17       4.12310562561766054982
               ==>

     ----------------
     ##7       <== 18       4.24264068711928514641
     ##3       ==> 18       4.24264705882352941176

     ##7       #:2   <== 4.24264068711928514641
     ##3       #:2   ==> 4.24264705882352941176
      Absolute error = 6.3717042443e-6, Relative error = 1.5018250929e-6
     ----------------
     ##8       <== 19       4.35889894354067355224
               ==>

     ----------------
     ##9       <== 20       4.47213595499957939282
               ==>

     ----------------
     ##10      <== 21       4.58257569495584000659
     ##4       ==> 21       4.58260869565217391304

     ##10      #:2   <== 4.58257569495584000659
     ##4       #:2   ==> 4.58260869565217391304
      Absolute error = 3.3000696334e-5, Relative error = 7.2013423303e-6
     ----------------
     ##11      <== 22       4.69041575982342955457
               ==>

     ----------------
     ##12      <== 23       4.7958315233127195416
               ==>

     ----------------
     ##13      <== 24       4.89897948556635619639
               ==>


     +++  File "list1" differs from file "list2"

   Numdiff has recognized that the lines of 'list1' with the square
roots for the numbers 13, 14, 16, 17, 19, 20, 22, 23, and 24 have been
deleted from 'list2'.  The numerical comparison has been done by
coupling each line of 'list2' with the line of 'list1' which displays
the square root for the same integer value.  The output obtained running
the filter of Numdiff via 'numdiff -f -z 2- list1 list2' confirms this:
     12       3.46410161513775458705         12       3.46410162002945508100
     13       3.60555127546398929312      <
     14       3.74165738677394138558      <
     15       3.87298334620741688518         15       3.87298387096774193548
     16       4                           <
     17       4.12310562561766054982      <
     18       4.24264068711928514641         18       4.24264705882352941176
     19       4.35889894354067355224      <
     20       4.47213595499957939282      <
     21       4.58257569495584000659         21       4.58260869565217391304
     22       4.69041575982342955457      <
     23       4.7958315233127195416       <
     24       4.89897948556635619639      <


     +++  File "list1" differs from file "list2"

   If you compare the command 'numdiff -z 2- -V list1 list2' with the
one used for the files 'bill1' and 'bill2', *note command::, you surely
notice that the filter has been invoked in different ways, first with
'-z @' and then with '-z 2-'.

   The synchronization procedure used by the filter is based on blurring
and byte-by-byte comparison.  The options '-z' and '-Z' are used to
select which fields from which file have to be blurred.  They take both
an argument in the same form requested by '-X', *note Use of the option
-X::, but accept additionally the special value '@' as abbreviation for
the range of fields '1-'.  Thus, the specifications '1:@', '2:@' and '@'
are used to mean all fields of the first file, of the second one or of
both, respectively.

   Employing '-z' and '-Z' in the right way is extremely important to
let the filter work as desired.  For instance, 'numdiff -f -z @ list1
list2' matches the lines of 'list1' and 'list2' in the same wrong way
     12       3.46410161513775458705         12       3.46410162002945508100
     13       3.60555127546398929312         15       3.87298387096774193548
     14       3.74165738677394138558         18       4.24264705882352941176
     15       3.87298334620741688518         21       4.58260869565217391304
     16       4                           <
     17       4.12310562561766054982      <
     18       4.24264068711928514641      <
     19       4.35889894354067355224      <
     20       4.47213595499957939282      <
     21       4.58257569495584000659      <
     22       4.69041575982342955457      <
     23       4.7958315233127195416       <
     24       4.89897948556635619639      <


     +++  File "list1" differs from file "list2"

as Numdiff would do without employing the filter.

   It is essential then to understand what blurring a field means and
how the filter uses blurring to match the lines of the files to compare.

   After reading the files the filter removes from each of them (from
their images in the memory, actually) all the fields selected by the
option '-X', then it replaces each of the fields that have to be blurred
by a special character.  This special character is the same for both
files and it is so chosen that it cannot appear in the text.  Blurring a
field means to replace it by this sort of place card.

   After doing this, the filter converts all remaining numerical fields
to a standard format and then compares the files byte by byte neglecting
the field delimiters.  This comparison is just used to establish which
lines of the first file are not present in the second, which lines of
the second file are missing in the first one, and how to match the
remaining lines to create a one-to-one correspondence.

   Only at this point 'numdiff' inspects each couple of corresponding
lines, splits the two lines into the constituent fields, and neglecting
those ones eventually specified through the option '-X' compares
corresponding fields as it is supposed to do, performing a numerical
comparison whenever the fields are both legal numerical values.

   Blurring the right fields is essential to appropriately match the
lines from the two files before doing any numerical comparison.  Without
blurring, the numerical fields could prevent the filter of 'numdiff'
from an appropriate matching of the lines by creating confusion with
their (maybe small) numeric differences.

   Blurring can be of two types, conditional or unconditional.  The
blurring is conditional if it has to be performed only for fields which
turn out to be legal numerical values.  The arguments of the option '-z'
indicate which fields of which file have to be blurred *under the
condition that they are recognized as numeric fields*.  Non-numeric
fields are left by '-z' untouched (no blurring occurs for them).  Then
'-z 1:5-7' makes the filter blur the 5th, 6th and 7th field of each line
of the first file whenever they are recognized as numeric.

   By means of the option '-Z' you can specify which fields have to be
unconditionally blurred, i.e.  independently of their type, numeric or
not.  For example, '-Z 2:3-4' activates the blurring of the 3th and 4th
field of each line of the second file.

   Going back to the comparison of the files 'list1' and 'list2', the
option '-z 2-' of the command 'numdiff -z 2- -V list1 list2' makes the
filter transform the (memory copies of the) two files as
     12       *
     13       *
     14       *
     15       *
     16       *
     17       *
     18       *
     19       *
     20       *
     21       *
     22       *
     23       *
     24       *

and

     12       *
     15       *
     18       *
     21       *

respectively.  Here * denotes the special symbol used by the filter in
the blurring procedure, even if this symbol is not actually a bullet.
Since in this example space, tab and newline are used as field
delimiters, the byte-by-byte comparison between the transformed files
produces the same result displayed by the command 'sdiff -W' when
applied to them:

     12       *                        12       *
     13       *                     <
     14       *                     <
     15       *                        15       *
     16       *                     <
     17       *                     <
     18       *                        18       *
     19       *                     <
     20       *                     <
     21       *                        21       *
     22       *                     <
     23       *                     <
     24       *                     <

If you put the blurred fields back you obtain exactly the output of
'numdiff -f -z 2- list1 list2', i.e.  the outcome of the filtering:

     12       3.46410161513775458705           12       3.46410162002945508100
     13       3.60555127546398929312        <
     14       3.74165738677394138558        <
     15       3.87298334620741688518           15       3.87298387096774193548
     16       4                             <
     17       4.12310562561766054982        <
     18       4.24264068711928514641           18       4.24264705882352941176
     19       4.35889894354067355224        <
     20       4.47213595499957939282        <
     21       4.58257569495584000659           21       4.58260869565217391304
     22       4.69041575982342955457        <
     23       4.7958315233127195416         <
     24       4.89897948556635619639        <


     +++  File "list1" differs from file "list2"


Since the second field is a numerical value in all lines of 'list1' and
'list2', using the option '-Z' instead of '-z' makes no difference in
this case.  The output of 'numdiff -f -Z 2- list1 list2' is then the
same of 'numdiff -f -z 2- list1 list2'.

   After this explanation you should also understand why 'numdiff -f -z
@ list1 list2' gives a wrong result.  Since also the first field is
always a numerical value, the option '-z @' makes the filter transform
the two given files as
     *       *
     *       *
     *       *
     *       *
     *       *
     *       *
     *       *
     *       *
     *       *
     *       *
     *       *
     *       *
     *       *

and

     *       *
     *       *
     *       *
     *       *

respectively, making then impossible to match the lines in a reasonable
way.

   We consider now a typical situation in which it is better to use '-Z'
in place of '-z'.  If file 'Table1' contains
-6 	 2.449490
-5 	 2.236068
-4 	 2.000000
-3 	 1.732051
-2 	 1.414214
-1       1.000000
0        0
- - - - - - - - -
1 	 1.000000
2 	 1.414214
3 	 1.732051
4 	 2.000000
- - - - - - - - -
5 	 2.236068
6 	 2.449490
7 	 2.645751
- - - - - - - - -
8 	 2.828427
9 	 3.000000
10 	 3.162278
11 	 3.316625
12 	 3.464102
- - - - - - - - -
- - - - - - - - -
13 	 3.605551
14 	 3.741657

and 'Table2' contains

-6       Not_defined
-4       Not_defined
-2       Not_defined
 0       0.000000
 2 	 1.414216
 4 	 2.000000
 6 	 2.449494
 8 	 2.828469
 10 	 3.162278
 12 	 3.464102
 14 	 3.741658
********************END

then the output of 'numdiff -z 1:2 -Z 2:2 -f Table1 Table2' is
     -6       2.449490               -6       Not_defined
     -5       2.236068            <
     -4       2.000000               -4       Not_defined
     -3       1.732051            <
     -2       1.414214               -2       Not_defined
     -1       1.000000            <
     0        0                       0       0.000000
     - - - - - - - - -            <
     1        1.000000            <
     2        1.414214                2       1.414216
     3        1.732051            <
     4        2.000000                4       2.000000
     - - - - - - - - -            <
     5        2.236068            <
     6        2.449490                6       2.449494
     7        2.645751            <
     - - - - - - - - -            <
     8        2.828427                8       2.828469
     9        3.000000            <
     10       3.162278                10      3.162278
     11       3.316625            <
     12       3.464102                12      3.464102
     - - - - - - - - -            <
     - - - - - - - - -            <
     13       3.605551            <
     14       3.741657                14      3.741658
                                  >  ********************END


     +++  File "Table1" differs from file "Table2"

which is exactly what is expected.  On the other hand the command
'numdiff -z 2 -f Table1 Table2' displays
     -6       2.449490            |  -6       Not_defined
     -5       2.236068            |  -4       Not_defined
     -4       2.000000            |  -2       Not_defined
     -3       1.732051            <
     -2       1.414214            <
     -1       1.000000            <
     0        0                       0       0.000000
     - - - - - - - - -            <
     1        1.000000            <
     2        1.414214                2       1.414216
     3        1.732051            <
     4        2.000000                4       2.000000
     - - - - - - - - -            <
     5        2.236068            <
     6        2.449490                6       2.449494
     7        2.645751            <
     - - - - - - - - -            <
     8        2.828427                8       2.828469
     9        3.000000            <
     10       3.162278                10      3.162278
     11       3.316625            <
     12       3.464102                12      3.464102
     - - - - - - - - -            <
     - - - - - - - - -            <
     13       3.605551            <
     14       3.741657                14      3.741658
                                  >  ********************END


     +++  File "Table1" differs from file "Table2"

which is partially wrong.

   Notice that in 'Table1' you find (truncated to the sixth decimal
digit) the square roots of the absolute values of the integer numbers
between -6 and 20, plus some randomly added lines.  The file 'Table2'
contains approximations (obtained by Newton's method) of the square
roots of the even numbers between -6 and 20.  Since the (real) square
root is not defined for negative numbers, the values corresponding to
-6, -4 and -2 are replaced by Not_defined.

   Since Not_defined is not a numeric value, during the execution of the
last command the filter transforms 'Table1' in this way
     -6       *
     -5       *
     -4       *
     -3       *
     -2       *
     -1       *
     0        *
     - - - - - - - - -
     1        *
     2        *
     3        *
     4        *
     - - - - - - - - -
     5        *
     6        *
     7        *
     - - - - - - - - -
     8        *
     9        *
     10       *
     11       *
     12       *
     - - - - - - - - -
     - - - - - - - - -
     13       *
     14       *

and 'Table2' in this other way

     -6       Not_defined
     -4       Not_defined
     -2       Not_defined
      0       *
      2       *
      4       *
      6       *
      8       *
      10      *
      12      *
      14      *
     ********************END

Unfortunately the first three lines are enough to confuse the
synchronization procedure of the filter, which is based on a
byte-by-byte comparison with exclusion of the field delimiters, as
explained before.

   You can check that this is definitely the case by looking at the
output of the command 'sdiff -W' on the transformed files, which is
     -6       *           |  -6       Not_defined
     -5       *           |  -4       Not_defined
     -4       *           |  -2       Not_defined
     -3       *           <
     -2       *           <
     -1       *           <
     0        *               0       *
     - - - - - - - - -    <
     1        *           <
     2        *               2       *
     3        *           <
     4        *               4       *
     - - - - - - - - -    <
     5        *           <
     6        *               6       *
     7        *           <
     - - - - - - - - -    <
     8        *               8       *
     9        *           <
     10       *               10      *
     11       *           <
     12       *               12      *
     - - - - - - - - -    <
     - - - - - - - - -    <
     13       *           <
     14       *               14      *
                          >  ********************END

   If we give the command 'numdiff -z 1:2 -Z 2:2 -f Table1 Table2'
instead of 'numdiff -z 2 -f Table1 Table2', the second field of the
lines of 'Table2' is always blurred.  The filter transforms then
'Table2' into
     -6       *
     -4       *
     -2       *
      0       *
      2       *
      4       *
      6       *
      8       *
      10      *
      12      *
      14      *
     ********************END

and re-synchronizes the files 'Table1' and 'Table2' in the right way.

   Using the unconditional blurring is suggested in all cases when a
certain field, which you want to include in the comparison (use '-X' to
completely neglect one or more fields), is of numeric type in almost all
lines of (one of) the given files.  This can be for instance the case
when in some lines the contents of the field are given by a special
numeric value, like Infinity, Inf, +Inf or -Inf, or by NaN, abbreviation
for Not a Number.

   Concerning the numeric fields which are not blurred, it is worth
remarking that the filter is not confused by differences in the numeric
format.  Before the byte-by-byte comparison, numeric values are
converted indeed to a standard format.  To offer an example of this, let
us suppose that 'short1' contains a list of numbers with their
logarithms
0.001          -3
0.01           -2
0.1            -1
1               0
1000            3
1000000         6
1000000000      9

and 'short2' the same list of numbers and logarithms, but with
differences in the numeric format:
******************
0.0010000       -3
.0100           -2
0000.10         -1
1.               0
1,000.000        3
1,000,000.       6
1,000,000,000    9

Then 'numdiff -f -z 2- short1 short2' displays
                                  >  ******************
     0.001          -3               0.0010000       -3
     0.01           -2               .0100           -2
     0.1            -1               0000.10         -1
     1               0               1.               0
     1000            3               1,000.000        3
     1000000         6               1,000,000.       6
     1000000000      9               1,000,000,000    9


     +++  File "short1" differs from file "short2"

showing that the filter has matched the lines in the right way.

   The filter can even handle the case when the same numerical value is
written in decimal notation in one file and in scientific notation in
the other one.  If the files 'decimal' and 'scientific' contain
.001           -3
.01            -2
.1             -1
* * * * * * * * *
1               0
1000            3
1000000         6
1000000000      9

and
*****************
1.0e-3         -3
1.0e-2         -2
1.0e-1         -1
1.0e0           0
1.0e3           3
1.0e6           6
1.0e9           9
*****************

respectively, then 'numdiff -f -z 2- decimal scientific' prints
                                  >  *****************
     .001           -3               1.0e-3         -3
     .01            -2               1.0e-2         -2
     .1             -1               1.0e-1         -1
     * * * * * * * * *            <
     1               0               1.0e0           0
     1000            3               1.0e3           3
     1000000         6               1.0e6           6
     1000000000      9               1.0e9           9
                                  >  *****************


     +++  File "decimal" differs from file "scientific"

proving that the filter does not get confused.

   No problems arise also in the case when for the same field the
scientific notation is used in both files.  If the files 'sc1' and 'sc2'
contain
  1.E-3          -3
  1.00E-2        -2
  1.0E-1         -1
  1.0000E0        0
001.0E3           3
+01.000E6         6
  1.0E+09         9
  1.0E+10        10
* * * * * * * * * *

and
*****************
 1.0e-003      -3
 1.0e-2        -2
 1.0e-1        -1
 1.0e0          0
+1.0e3          3
 1.0e+6         6
 1.0e9          9

respectively, then 'numdiff -f -z 2- sc1 sc2' correctly displays
                                  >  *****************
       1.E-3          -3              1.0e-003      -3
       1.00E-2        -2              1.0e-2        -2
       1.0E-1         -1              1.0e-1        -1
       1.0000E0        0              1.0e0          0
     001.0E3           3             +1.0e3          3
     +01.000E6         6              1.0e+6         6
       1.0E+09         9              1.0e9          9
       1.0E+10        10          <
     * * * * * * * * * *          <


     +++  File "sc1" differs from file "sc2"

   The filter can even handle an improper use of the scientific
notation, meaning for example that it can recognize '123.456E+2' and
'1.23456E+4' as equal.

   We can see this in the case of the files 'Scnot1':
-------------------------
1.2E0             *     1
2.45E-1           *     2
-3.678E-2         *     3

and 'Scnot2':
12E-1             *     1
245E-3            *     2
-0.003678E+1      *     3

'numdiff -f -z 3- Scnot1 Scnot2' displays the report:
     -------------------------    <
     1.2E0             *     1       12E-1             *     1
     2.45E-1           *     2       245E-3            *     2
     -3.678E-2         *     3       -0.003678E+1      *     3


     +++  File "Scnot1" differs from file "Scnot2"

which is exactly what you would expect in such a case.  Also pretty hard
cases do not confuse the filter.  If 'Scnot1' is given by
 1.2000e0         *     1
02.4500e-1        *     2
-003.678E-2       *     3

and 'Scnot2' is the same file as before, the output of the command
'numdiff -f -z 3- Scnot1 Scnot2' is still right:
      1.2000e0         *     1       12E-1             *     1
     02.4500e-1        *     2       245E-3            *     2
     -003.678E-2       *     3       -0.003678E+1      *     3


     +++  Files "Scnot1" and "Scnot2" have the same structure

   In all examples above the option '-f' is used with no argument.

   However, '-f' accepts an optional argument, which can be used to
control how '-f' displays its output.  If you provide an argument, care
not to leave any space between the option and the argument: '-f60' is
correct while '-f 60' makes Numdiff terminate after printing an error
message.

   If the argument is a positive number NUM, then the side-by-side
output produced by '-f' will be NUM columns wide.  The default value for
the width of the output is 130, which can fit onto a traditional printer
line, and is the one used when '-f' has no argument, or the supplied
argument is zero.  In other words, '-f' and '-f0' are just easier to
remind versions of '-f130'.

   A negative argument has the same effect as the positive argument with
the same absolute value, but it causes in addition the removal of common
lines from the output.  For example, the command 'numdiff -z 1:2 -Z 2:2
-f-130 Table1 Table2' displays the following text
     -5       2.236068            <
     -3       1.732051            <
     -1       1.000000            <
     - - - - - - - - -            <
     1        1.000000            <
     3        1.732051            <
     - - - - - - - - -            <
     5        2.236068            <
     7        2.645751            <
     - - - - - - - - -            <
     9        3.000000            <
     11       3.316625            <
     - - - - - - - - -            <
     - - - - - - - - -            <
     13       3.605551            <
                                  >  ********************END


     +++  File "Table1" differs from file "Table2"

   In conjunction with the option '-f' or '-O' you can use '-T' to
expand tabs to spaces in the produced output.  This is useful to
preserve the alignment of tabs in the input files, if it is thrown off
by the presence of the gutter.

   The options '-H' and '-m' affect the performance of the filter of
Numdiff.  But performance has more than one dimension and these options
improve one aspect of performance at the cost of another, or they
improve performance in some cases while hurting it in others.

   The re-synchronization of the two compared files made by the filter
always comes up with a near-minimal set of deletions/insertions of
lines, that usually is good enough for practical purposes.  If the
filter displays a large set of line deletions/insertions, you might want
it to use a modified algorithm that sometimes produces a smaller set of
differences.  The '-m' option does this; however, it can also cause the
filter to run more slowly than usual, so it is not the default behavior.

   If the files you are comparing are large and have small groups of
changes scattered throughout them, you can use the '-H' option to make a
different modification to the algorithm employed by the filter.  If the
input files have a constant small density of changes, where change means
here deletion/insertion of lines, this option speeds up the comparison
without changing the output or in the worst case introducing minor
modifications.

9 Warnings
**********

   * Bug reports have to be sent to the address
     <ivprimi(at)libero(dot)it> .  Please, put Numdiff in the subject
     and indicate the version of the operating system you are running
     (in particular, do not forget to specify if it is a 32- or a 64-bit
     system), and, if you know it, the version of the compiler used to
     build Numdiff.  Please write also whether your version of Numdiff
     uses the GNU MP library or not.  Before writing an email be sure to
     run the latest stable version of Numdiff, I do not provide support
     for older versions.

   * Numdiff does not accept numbers in scientific notation whose
     exponents lie outside the range -1073741824, ..., +1073741824.  If
     such a number is found in any of the files to compare, the
     execution of the program is stopped after printing a suitable error
     message on stderr.  Under the assumption that the numeric format in
     use is the default one, with "1.0001e-2147483640" the displayed
     error messages is
          numdiff: A number with a too small exponent has been found,
          namely "1.0001e-2147483640".
          Exponents smaller than -1073741824 are not accepted,
          the execution of the program ends now

   * If Numdiff has been built with its own internal support for
     multiple precision arithmetic instead of being linked against the
     GNU MP Library, then performance degradation and memory exhaustion
     can already make impossible to handle exponents of magnitude 10^6 =
     1000000.  This is what I obtained on my laptop, equipped with a
     dual core processor @1.50 GHz and with 1GB of RAM, when I tried to
     compare the numbers 1.101e1000000000 and 1.0e1000000000:
          numdiff: Insufficient memory for new allocation,
          the execution of the program ends now
     In addition, you can overload the processor with numbers whose
     exponents lie outside the range -1000000, ..., 1000000.  But at
     least on my machine, everything works fine and quick enough as long
     as exponent and size of the mantissa of the numbers are in the
     range -1000, ..., 1000.  Be careful and remember that Numdiff is
     distributed WITHOUT ANY WARRANTY; without even the implied warranty
     of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

     Consider also that, if you have numeric data with exponents outside
     the range -300, ..., 300, probably there is something wrong with
     your data: either you are using the wrong scale, or you should
     replace very small numbers, like 1e-100, by zero, or it is quite
     likely that the machine/program/algorithm which produced these data
     is not working right.

   * If Numdiff has been linked against the GNU Multiple Precision
     Arithmetic Library (also called GNU MP), then the precision it uses
     is typically higher than the specified one.  On my machine the
     actual value of the precision is 20 if the user gives a value
     between 0 and 20, 30 if the user specifies a precision between 21
     and 30, 40 for a user-specified value between 31 and 40, and so on.
     Anyway, the actual precision is never less than the one required by
     the user.

   * After reading a numeric field, Numdiff truncates its value if this
     number has too much digits with respect to the current precision.
     To be precise, denoted by P the current value of the precision, the
     following rules apply.

     If 'numdiff' has been built with its own internal support for
     multiple precision arithmetic, then
        * if the number is written in ordinary decimal notation,
          'numdiff' will consider, in addition to all digits of the
          integer part, only the first P digits of the fractional part;
        * if the value is written in scientific notation, then 'numdiff'
          will only consider the first P digits of the fractional part
          of the mantissa.

     If 'numdiff' uses the GNU MP library to perform its computations,
     the value of a numeric field is first translated into scientific
     notation and then only the first P digits of the fractional part of
     the mantissa are considered.

     By current value of the precision I mean the integer value
     specified by the option '-#', or the default one (35) when this
     option is not in use.

   * You can find out whether your local version of 'numdiff' is relying
     on GNU MP or not by executing the command 'numdiff -v'.  If
     'numdiff' uses GNU MP, then this command will display the following
     message or similar (possibly translated into your mother language)
     among other information:
          The software has been linked against
          the GNU Multiple Precision Arithmetic Library,
          version number 4.2.4.

     If 'numdiff' does not rely on GNU MP, then the displayed message
     will be (up to translation into your mother language)
          The software has been built with
          its own internal support for multiple precision arithmetic.

   * Numdiff can only be used on text files: the program terminates
     after printing a suitable error message if one of the files to
     compare turns out to be a binary file.  To detect if a file is
     binary or not, 'numdiff' checks for the presence of null bytes
     (0x00) in the file.

   * If you are not including the so called white-space characters
     (usually ' ', '\t', '\f', '\v' and '\r') in the set of field
     delimiters, then a real and an imaginary number which are separated
     just by white-spaces can be coupled together and considered as a
     whole complex number.  For example, if you are using only *colon*
     (':') and *newline* as field delimiters and Numdiff finds a line
     like that
     ::::3.0-5.6e-356i::::-12.9   +4.34i::::-12.9    4.34i::::New York::::

     then it will consider this line as formed by four fields, the first
     two are numeric and given by the complex numbers 3.0-5.6e-356i and
     -12.9+4.34i, the last two ones are the strings New York and
     -12.9    4.34i.  I still do not know if I will modify this in the
     next version of Numdiff, so that the program recognizes only
     3.0-5.6e-356i as numeric field and treats -12.9   +4.34i as
     non-numeric due to the presence of spaces in the middle.
     -12.9    4.34i is already considered as non-numeric due to the
     absence of a leading sign in the imaginary value.

   * We have seen that one of the two files passed to 'numdiff' can be
     -, which refers to stdin (standard input).  In this way one of the
     two files to compare can be the output produced by another command,
     like in 'cat file2 | numdiff -a 1.0e-3 file1 -'.  However, if you
     activate the filter by means of the options '-z' or/and '-Z',
     Numdiff can not work with the standard input unless you use also
     the option '-f'.  Therefore, the command 'cat file2 | numdiff -a
     1.0e-3 -z @ file1 -' displays only the error message
     numdiff: -: Illegal seek
     (or maybe the translation of this message in the language you are
     using on your computer) but 'cat file2 | numdiff -a 1.0e-3 -z @ -f
     file1 -' works as expected.

   * This manual describes the version 5.9 of Numdiff.  Prior 5.x
     versions did not recognize all the options that are currently
     accepted, versions 4.0.0 and 3.x used even a different format for
     the output.

Appendix A GNU Free Documentation License
*****************************************

                     Version 1.3, 3 November 2008

     Copyright (C) 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
     <http://fsf.org/>

     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.

  0. PREAMBLE

     The purpose of this License is to make a manual, textbook, or other
     functional and useful document "free" in the sense of freedom: to
     assure everyone the effective freedom to copy and redistribute it,
     with or without modifying it, either commercially or
     noncommercially.  Secondarily, this License preserves for the
     author and publisher a way to get credit for their work, while not
     being considered responsible for modifications made by others.

     This License is a kind of "copyleft", which means that derivative
     works of the document must themselves be free in the same sense.
     It complements the GNU General Public License, which is a copyleft
     license designed for free software.

     We have designed this License in order to use it for manuals for
     free software, because free software needs free documentation: a
     free program should come with manuals providing the same freedoms
     that the software does.  But this License is not limited to
     software manuals; it can be used for any textual work, regardless
     of subject matter or whether it is published as a printed book.  We
     recommend this License principally for works whose purpose is
     instruction or reference.

  1. APPLICABILITY AND DEFINITIONS

     This License applies to any manual or other work, in any medium,
     that contains a notice placed by the copyright holder saying it can
     be distributed under the terms of this License.  Such a notice
     grants a world-wide, royalty-free license, unlimited in duration,
     to use that work under the conditions stated herein.  The
     "Document", below, refers to any such manual or work.  Any member
     of the public is a licensee, and is addressed as "you".  You accept
     the license if you copy, modify or distribute the work in a way
     requiring permission under copyright law.

     A "Modified Version" of the Document means any work containing the
     Document or a portion of it, either copied verbatim, or with
     modifications and/or translated into another language.

     A "Secondary Section" is a named appendix or a front-matter section
     of the Document that deals exclusively with the relationship of the
     publishers or authors of the Document to the Document's overall
     subject (or to related matters) and contains nothing that could
     fall directly within that overall subject.  (Thus, if the Document
     is in part a textbook of mathematics, a Secondary Section may not
     explain any mathematics.)  The relationship could be a matter of
     historical connection with the subject or with related matters, or
     of legal, commercial, philosophical, ethical or political position
     regarding them.

     The "Invariant Sections" are certain Secondary Sections whose
     titles are designated, as being those of Invariant Sections, in the
     notice that says that the Document is released under this License.
     If a section does not fit the above definition of Secondary then it
     is not allowed to be designated as Invariant.  The Document may
     contain zero Invariant Sections.  If the Document does not identify
     any Invariant Sections then there are none.

     The "Cover Texts" are certain short passages of text that are
     listed, as Front-Cover Texts or Back-Cover Texts, in the notice
     that says that the Document is released under this License.  A
     Front-Cover Text may be at most 5 words, and a Back-Cover Text may
     be at most 25 words.

     A "Transparent" copy of the Document means a machine-readable copy,
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     "Transparent" is called "Opaque".

     Examples of suitable formats for Transparent copies include plain
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     Examples of transparent image formats include PNG, XCF and JPG.
     Opaque formats include proprietary formats that can be read and
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     processors for output purposes only.

     The "Title Page" means, for a printed book, the title page itself,
     plus such following pages as are needed to hold, legibly, the
     material this License requires to appear in the title page.  For
     works in formats which do not have any title page as such, "Title
     Page" means the text near the most prominent appearance of the
     work's title, preceding the beginning of the body of the text.

     The "publisher" means any person or entity that distributes copies
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     A section "Entitled XYZ" means a named subunit of the Document
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     To "Preserve the Title" of such a section when you modify the
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     The Document may include Warranty Disclaimers next to the notice
     which states that this License applies to the Document.  These
     Warranty Disclaimers are considered to be included by reference in
     this License, but only as regards disclaiming warranties: any other
     implication that these Warranty Disclaimers may have is void and
     has no effect on the meaning of this License.

  2. VERBATIM COPYING

     You may copy and distribute the Document in any medium, either
     commercially or noncommercially, provided that this License, the
     copyright notices, and the license notice saying this License
     applies to the Document are reproduced in all copies, and that you
     add no other conditions whatsoever to those of this License.  You
     may not use technical measures to obstruct or control the reading
     or further copying of the copies you make or distribute.  However,
     you may accept compensation in exchange for copies.  If you
     distribute a large enough number of copies you must also follow the
     conditions in section 3.

     You may also lend copies, under the same conditions stated above,
     and you may publicly display copies.

  3. COPYING IN QUANTITY

     If you publish printed copies (or copies in media that commonly
     have printed covers) of the Document, numbering more than 100, and
     the Document's license notice requires Cover Texts, you must
     enclose the copies in covers that carry, clearly and legibly, all
     these Cover Texts: Front-Cover Texts on the front cover, and
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     front cover must present the full title with all words of the title
     equally prominent and visible.  You may add other material on the
     covers in addition.  Copying with changes limited to the covers, as
     long as they preserve the title of the Document and satisfy these
     conditions, can be treated as verbatim copying in other respects.

     If the required texts for either cover are too voluminous to fit
     legibly, you should put the first ones listed (as many as fit
     reasonably) on the actual cover, and continue the rest onto
     adjacent pages.

     If you publish or distribute Opaque copies of the Document
     numbering more than 100, you must either include a machine-readable
     Transparent copy along with each Opaque copy, or state in or with
     each Opaque copy a computer-network location from which the general
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     network protocols a complete Transparent copy of the Document, free
     of added material.  If you use the latter option, you must take
     reasonably prudent steps, when you begin distribution of Opaque
     copies in quantity, to ensure that this Transparent copy will
     remain thus accessible at the stated location until at least one
     year after the last time you distribute an Opaque copy (directly or
     through your agents or retailers) of that edition to the public.

     It is requested, but not required, that you contact the authors of
     the Document well before redistributing any large number of copies,
     to give them a chance to provide you with an updated version of the
     Document.

  4. MODIFICATIONS

     You may copy and distribute a Modified Version of the Document
     under the conditions of sections 2 and 3 above, provided that you
     release the Modified Version under precisely this License, with the
     Modified Version filling the role of the Document, thus licensing
     distribution and modification of the Modified Version to whoever
     possesses a copy of it.  In addition, you must do these things in
     the Modified Version:

       A. Use in the Title Page (and on the covers, if any) a title
          distinct from that of the Document, and from those of previous
          versions (which should, if there were any, be listed in the
          History section of the Document).  You may use the same title
          as a previous version if the original publisher of that
          version gives permission.

       B. List on the Title Page, as authors, one or more persons or
          entities responsible for authorship of the modifications in
          the Modified Version, together with at least five of the
          principal authors of the Document (all of its principal
          authors, if it has fewer than five), unless they release you
          from this requirement.

       C. State on the Title page the name of the publisher of the
          Modified Version, as the publisher.

       D. Preserve all the copyright notices of the Document.

       E. Add an appropriate copyright notice for your modifications
          adjacent to the other copyright notices.

       F. Include, immediately after the copyright notices, a license
          notice giving the public permission to use the Modified
          Version under the terms of this License, in the form shown in
          the Addendum below.

       G. Preserve in that license notice the full lists of Invariant
          Sections and required Cover Texts given in the Document's
          license notice.

       H. Include an unaltered copy of this License.

       I. Preserve the section Entitled "History", Preserve its Title,
          and add to it an item stating at least the title, year, new
          authors, and publisher of the Modified Version as given on the
          Title Page.  If there is no section Entitled "History" in the
          Document, create one stating the title, year, authors, and
          publisher of the Document as given on its Title Page, then add
          an item describing the Modified Version as stated in the
          previous sentence.

       J. Preserve the network location, if any, given in the Document
          for public access to a Transparent copy of the Document, and
          likewise the network locations given in the Document for
          previous versions it was based on.  These may be placed in the
          "History" section.  You may omit a network location for a work
          that was published at least four years before the Document
          itself, or if the original publisher of the version it refers
          to gives permission.

       K. For any section Entitled "Acknowledgements" or "Dedications",
          Preserve the Title of the section, and preserve in the section
          all the substance and tone of each of the contributor
          acknowledgements and/or dedications given therein.

       L. Preserve all the Invariant Sections of the Document, unaltered
          in their text and in their titles.  Section numbers or the
          equivalent are not considered part of the section titles.

       M. Delete any section Entitled "Endorsements".  Such a section
          may not be included in the Modified Version.

       N. Do not retitle any existing section to be Entitled
          "Endorsements" or to conflict in title with any Invariant
          Section.

       O. Preserve any Warranty Disclaimers.

     If the Modified Version includes new front-matter sections or
     appendices that qualify as Secondary Sections and contain no
     material copied from the Document, you may at your option designate
     some or all of these sections as invariant.  To do this, add their
     titles to the list of Invariant Sections in the Modified Version's
     license notice.  These titles must be distinct from any other
     section titles.

     You may add a section Entitled "Endorsements", provided it contains
     nothing but endorsements of your Modified Version by various
     parties--for example, statements of peer review or that the text
     has been approved by an organization as the authoritative
     definition of a standard.

     You may add a passage of up to five words as a Front-Cover Text,
     and a passage of up to 25 words as a Back-Cover Text, to the end of
     the list of Cover Texts in the Modified Version.  Only one passage
     of Front-Cover Text and one of Back-Cover Text may be added by (or
     through arrangements made by) any one entity.  If the Document
     already includes a cover text for the same cover, previously added
     by you or by arrangement made by the same entity you are acting on
     behalf of, you may not add another; but you may replace the old
     one, on explicit permission from the previous publisher that added
     the old one.

     The author(s) and publisher(s) of the Document do not by this
     License give permission to use their names for publicity for or to
     assert or imply endorsement of any Modified Version.

  5. COMBINING DOCUMENTS

     You may combine the Document with other documents released under
     this License, under the terms defined in section 4 above for
     modified versions, provided that you include in the combination all
     of the Invariant Sections of all of the original documents,
     unmodified, and list them all as Invariant Sections of your
     combined work in its license notice, and that you preserve all
     their Warranty Disclaimers.

     The combined work need only contain one copy of this License, and
     multiple identical Invariant Sections may be replaced with a single
     copy.  If there are multiple Invariant Sections with the same name
     but different contents, make the title of each such section unique
     by adding at the end of it, in parentheses, the name of the
     original author or publisher of that section if known, or else a
     unique number.  Make the same adjustment to the section titles in
     the list of Invariant Sections in the license notice of the
     combined work.

     In the combination, you must combine any sections Entitled
     "History" in the various original documents, forming one section
     Entitled "History"; likewise combine any sections Entitled
     "Acknowledgements", and any sections Entitled "Dedications".  You
     must delete all sections Entitled "Endorsements."

  6. COLLECTIONS OF DOCUMENTS

     You may make a collection consisting of the Document and other
     documents released under this License, and replace the individual
     copies of this License in the various documents with a single copy
     that is included in the collection, provided that you follow the
     rules of this License for verbatim copying of each of the documents
     in all other respects.

     You may extract a single document from such a collection, and
     distribute it individually under this License, provided you insert
     a copy of this License into the extracted document, and follow this
     License in all other respects regarding verbatim copying of that
     document.

  7. AGGREGATION WITH INDEPENDENT WORKS

     A compilation of the Document or its derivatives with other
     separate and independent documents or works, in or on a volume of a
     storage or distribution medium, is called an "aggregate" if the
     copyright resulting from the compilation is not used to limit the
     legal rights of the compilation's users beyond what the individual
     works permit.  When the Document is included in an aggregate, this
     License does not apply to the other works in the aggregate which
     are not themselves derivative works of the Document.

     If the Cover Text requirement of section 3 is applicable to these
     copies of the Document, then if the Document is less than one half
     of the entire aggregate, the Document's Cover Texts may be placed
     on covers that bracket the Document within the aggregate, or the
     electronic equivalent of covers if the Document is in electronic
     form.  Otherwise they must appear on printed covers that bracket
     the whole aggregate.

  8. TRANSLATION

     Translation is considered a kind of modification, so you may
     distribute translations of the Document under the terms of section
     4.  Replacing Invariant Sections with translations requires special
     permission from their copyright holders, but you may include
     translations of some or all Invariant Sections in addition to the
     original versions of these Invariant Sections.  You may include a
     translation of this License, and all the license notices in the
     Document, and any Warranty Disclaimers, provided that you also
     include the original English version of this License and the
     original versions of those notices and disclaimers.  In case of a
     disagreement between the translation and the original version of
     this License or a notice or disclaimer, the original version will
     prevail.

     If a section in the Document is Entitled "Acknowledgements",
     "Dedications", or "History", the requirement (section 4) to
     Preserve its Title (section 1) will typically require changing the
     actual title.

  9. TERMINATION

     You may not copy, modify, sublicense, or distribute the Document
     except as expressly provided under this License.  Any attempt
     otherwise to copy, modify, sublicense, or distribute it is void,
     and will automatically terminate your rights under this License.

     However, if you cease all violation of this License, then your
     license from a particular copyright holder is reinstated (a)
     provisionally, unless and until the copyright holder explicitly and
     finally terminates your license, and (b) permanently, if the
     copyright holder fails to notify you of the violation by some
     reasonable means prior to 60 days after the cessation.

     Moreover, your license from a particular copyright holder is
     reinstated permanently if the copyright holder notifies you of the
     violation by some reasonable means, this is the first time you have
     received notice of violation of this License (for any work) from
     that copyright holder, and you cure the violation prior to 30 days
     after your receipt of the notice.

     Termination of your rights under this section does not terminate
     the licenses of parties who have received copies or rights from you
     under this License.  If your rights have been terminated and not
     permanently reinstated, receipt of a copy of some or all of the
     same material does not give you any rights to use it.

  10. FUTURE REVISIONS OF THIS LICENSE

     The Free Software Foundation may publish new, revised versions of
     the GNU Free Documentation License from time to time.  Such new
     versions will be similar in spirit to the present version, but may
     differ in detail to address new problems or concerns.  See
     <http://www.gnu.org/copyleft/>.

     Each version of the License is given a distinguishing version
     number.  If the Document specifies that a particular numbered
     version of this License "or any later version" applies to it, you
     have the option of following the terms and conditions either of
     that specified version or of any later version that has been
     published (not as a draft) by the Free Software Foundation.  If the
     Document does not specify a version number of this License, you may
     choose any version ever published (not as a draft) by the Free
     Software Foundation.  If the Document specifies that a proxy can
     decide which future versions of this License can be used, that
     proxy's public statement of acceptance of a version permanently
     authorizes you to choose that version for the Document.

  11. RELICENSING

     "Massive Multiauthor Collaboration Site" (or "MMC Site") means any
     World Wide Web server that publishes copyrightable works and also
     provides prominent facilities for anybody to edit those works.  A
     public wiki that anybody can edit is an example of such a server.
     A "Massive Multiauthor Collaboration" (or "MMC") contained in the
     site means any set of copyrightable works thus published on the MMC
     site.

     "CC-BY-SA" means the Creative Commons Attribution-Share Alike 3.0
     license published by Creative Commons Corporation, a not-for-profit
     corporation with a principal place of business in San Francisco,
     California, as well as future copyleft versions of that license
     published by that same organization.

     "Incorporate" means to publish or republish a Document, in whole or
     in part, as part of another Document.

     An MMC is "eligible for relicensing" if it is licensed under this
     License, and if all works that were first published under this
     License somewhere other than this MMC, and subsequently
     incorporated in whole or in part into the MMC, (1) had no cover
     texts or invariant sections, and (2) were thus incorporated prior
     to November 1, 2008.

     The operator of an MMC Site may republish an MMC contained in the
     site under CC-BY-SA on the same site at any time before August 1,
     2009, provided the MMC is eligible for relicensing.

ADDENDUM: How to use this License for your documents
====================================================

To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and license
notices just after the title page:

       Copyright (C)  YEAR  YOUR NAME.
       Permission is granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version 1.3
       or any later version published by the Free Software Foundation;
       with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
       Texts.  A copy of the license is included in the section entitled ``GNU
       Free Documentation License''.

   If you have Invariant Sections, Front-Cover Texts and Back-Cover
Texts, replace the "with...Texts."  line with this:

         with the Invariant Sections being LIST THEIR TITLES, with
         the Front-Cover Texts being LIST, and with the Back-Cover Texts
         being LIST.

   If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
situation.

   If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of free
software license, such as the GNU General Public License, to permit
their use in free software.

Index
*****

* Menu:

* Acknowledgments:                       Acknowledgments.    (line   55)
* Build:                                 Installing.         (line 1031)
* Caveats:                               Warnings.           (line 3683)
* Command line options for ndselect:     Invoking ndselect.  (line 2867)
* Command line options for numdiff:      Invoking numdiff.   (line 1139)
* Compile:                               Installing.         (line 1031)
* Copying Conditions:                    Copying.            (line   39)
* Diagnostics (ndselect):                Invoking ndselect.  (line 2867)
* Diagnostics (numdiff):                 Invoking numdiff.   (line 1139)
* FDL:                                   GNU Free Documentation License.
                                                             (line 3821)
* Filter:                                Filtering.          (line 2959)
* Filter output (numdiff):               Filter output.      (line  957)
* Format of the reports:                 Output format.      (line  575)
* GNU FDL:                               GNU Free Documentation License.
                                                             (line 3821)
* GNU Free Documentation License:        GNU Free Documentation License.
                                                             (line 3821)
* GNU General Public License:            Copying.            (line   39)
* GPL:                                   Copying.            (line   39)
* How to use numdiff:                    Overview.           (line   71)
* Install:                               Installing.         (line 1031)
* Introduction:                          Overview.           (line   71)
* Invoking ndselect:                     Invoking ndselect.  (line 2867)
* Invoking numdiff:                      Invoking numdiff.   (line 1139)
* License:                               Copying.            (line   39)
* ndselect (introduction to its use):    ndselect.           (line 2734)
* Notes:                                 Warnings.           (line 3683)
* Options, command line (ndselect):      Invoking ndselect.  (line 2867)
* Options, command line (numdiff):       Invoking numdiff.   (line 1139)
* Output format (numdiff):               Output format.      (line  575)
* Overview mode of numdiff:              Overview mode.      (line  736)
* Predefined settings of numdiff:        Invoking numdiff.   (line 1139)
* Purposes:                              Overview.           (line   71)
* Raw output format:                     Raw output.         (line 1005)
* Side-by-side report (numdiff):         Overview mode.      (line  736)
* Synopsis (ndselect):                   Invoking ndselect.  (line 2867)
* Synopsis (numdiff):                    Invoking numdiff.   (line 1139)
* Thanks:                                Acknowledgments.    (line   55)
* Tools:                                 ndselect.           (line 2734)
* Usage of numdiff:                      Overview.           (line   71)
* Warnings:                              Warnings.           (line 3683)

