// $Id: compare_change.cpp 3757 2015-11-30 12:03:07Z bradbell $
/* --------------------------------------------------------------------------
CppAD: C++ Algorithmic Differentiation: Copyright (C) 2003-15 Bradley M. Bell

CppAD is distributed under multiple licenses. This distribution is under
the terms of the
                    GNU General Public License Version 3.

A copy of this license is included in the COPYING file of this distribution.
Please visit http://www.coin-or.org/CppAD/ for information on other licenses.
-------------------------------------------------------------------------- */

/*
$begin compare_change.cpp$$
$spell
	Cpp
$$

$section CompareChange and Re-Tape: Example and Test$$
$mindex compare change re-tape$$


$code
$verbatim%example/compare_change.cpp%0%// BEGIN C++%// END C++%1%$$
$$

$end
*/
// BEGIN C++

# include <cppad/cppad.hpp>

namespace { // put this function in the empty namespace
	template <typename Type>
	Type Minimum(const Type &x, const Type &y)
	{	// Use a comparision to compute the min(x, y)
		// (note that CondExp would never require retaping).
		if( x < y )
			return x;
		return y;
	}
	struct error_info {
		bool known;
		int  line;
		std::string file;
		std::string exp;
		std::string msg;
	};
	void error_handler(
		bool        known       ,
		int         line        ,
		const char *file        ,
		const char *exp         ,
		const char *msg         )
	{	// error handler must not return, so throw an exception
		error_info info;
		info.known = known;
		info.line  = line;
		info.file  = file;
		info.exp   = exp;
		info.msg   = msg;
		throw info;
	}

}

bool compare_change(void)
{	bool ok = true;
	using CppAD::AD;

	// domain space vector
	size_t n = 2;
	CPPAD_TESTVECTOR(AD<double>) ax(n);
	ax[0] = 3.;
	ax[1] = 4.;

	// declare independent variables and start tape recording
	CppAD::Independent(ax);

	// range space vector
	size_t m = 1;
	CPPAD_TESTVECTOR(AD<double>) ay(m);
	ay[0] = Minimum(ax[0], ax[1]);

	// create f: x -> y and stop tape recording
	CppAD::ADFun<double> f(ax, ay);

	// set count to one (not necessry because is its default value)
	f.compare_change_count(1);

	// evaluate zero mode Forward where comparison has the same result
	// as during taping; i.e., x[0] < x[1].
	CPPAD_TESTVECTOR(double) x(n), y(m);
	x[0] = 2.;
	x[1] = 3.;
	y    = f.Forward(0, x);
	ok  &= (y[0] == x[0]);
	ok  &= (y[0] == Minimum(x[0], x[1]));
	ok  &= (f.compare_change_number() == 0);
	ok  &= (f.compare_change_op_index() == 0);

	// evaluate zero mode Forward where comparison has different result
	// as during taping; i.e., x[0] >= x[1].
	x[0] = 3.;
	x[1] = 2.;
	y    = f.Forward(0, x);
	ok  &= (y[0] == x[0]);
	ok  &= (y[0] != Minimum(x[0], x[1]));
	ok  &= (f.compare_change_number() == 1);
	ok  &= (f.compare_change_op_index() > 0 );
	size_t op_index = f.compare_change_op_index();

	// Local block during which default CppAD error handler is replaced.
	// If you do not replace the default CppAD error handler,
	// and you run in the debugger, you will be able to inspect the
	// call stack and see that 'if( x < y )' is where the comparison is.
	bool missed_error = true;
	{	CppAD::ErrorHandler local_error_handler(error_handler);

		std::string check_msg =
			"Operator index equals abort_op_index in Independent";
		try {
			// determine the operation index where the change occurred
			CppAD::Independent(ax, op_index);
			ay[0] = Minimum(ax[0], ax[1]);
# ifdef NDEBUG
			// CppAD does not spend time checking operator index when
			// NDEBUG is defined
			missed_error = false;
			AD<double>::abort_recording();
# endif
		}
		catch( error_info info )
		{	missed_error = false;
			ok          &= info.known;
			ok          &= info.msg == check_msg;
			// Must abort the recording so we can start a new one
			// (and to avoid a memory leak).
			AD<double>::abort_recording();
		}
	}
	ok &= ! missed_error;


	// set count to zero to demonstrate case where comparisons are not checked
	f.compare_change_count(0);
	y    = f.Forward(0, x);
	ok  &= (y[0] == x[0]);
	ok  &= (y[0] != Minimum(x[0], x[1]));
	ok  &= (f.compare_change_number()   == 0);
	ok  &= (f.compare_change_op_index() == 0);

	// now demonstrate that compare_change_number works for an optimized
	// tape (note that compare_change_op_index is always zero after optimize)
	f.optimize();
	f.compare_change_count(1);
	y    = f.Forward(0, x);
	ok  &= (y[0] == x[0]);
	ok  &= (y[0] != Minimum(x[0], x[1]));
	ok  &= (f.compare_change_number()   == 1);
	ok  &= (f.compare_change_op_index() == 0);

	// now retape to get the a tape that agrees with the algorithm
	ax[0] = x[0];
	ax[1] = x[1];
	Independent(ax);
	ay[0] = Minimum(ax[0], ax[1]);
	f.Dependent(ax, ay);
	y    = f.Forward(0, x);
	ok  &= (y[0] == x[1]);
	ok  &= (y[0] == Minimum(x[0], x[1]));
	ok  &= (f.compare_change_number()   == 0);
	ok  &= (f.compare_change_op_index() == 0);

	return ok;
}


// END C++
