// $Id: exp_eps_rev1.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 exp_eps_rev1.cpp$$
$spell
	cstddef
	cmath
	vars
	ir
	iq
	ir
	ia
	df
	exp_eps_rev
	bool
	std
	fabs
$$

$section exp_eps: Verify First Order Reverse Sweep$$
$mindex exp_eps$$


$codep */
# include <cstddef>                     // define size_t
# include <cmath>                       // for fabs function
extern bool exp_eps_for0(double *v0);   // computes zero order forward sweep
bool exp_eps_rev1(void)
{	bool ok = true;

	// set the value of v0[j] for j = 1 , ... , 7
	double v0[8];
	ok &= exp_eps_for0(v0);

	// initial all partial derivatives as zero
	double f_v[8];
	size_t j;
	for(j = 0; j < 8; j++)
		f_v[j] = 0.;

	// set partial derivative for f7
	f_v[7] = 1.;
	ok    &= std::fabs( f_v[7] - 1. ) <= 1e-10;     // f7_v7

	// f6( v1 , v2 , v3 , v4 , v5 , v6 )
	f_v[4] += f_v[7] * 1.;
	f_v[6] += f_v[7] * 1.;
	ok     &= std::fabs( f_v[4] - 1.  ) <= 1e-10;   // f6_v4
	ok     &= std::fabs( f_v[6] - 1.  ) <= 1e-10;   // f6_v6

	// f5( v1 , v2 , v3 , v4 , v5 )
	f_v[5] += f_v[6] / 2.;
	ok     &= std::fabs( f_v[5] - 0.5 ) <= 1e-10;   // f5_v5

	// f4( v1 , v2 , v3 , v4 )
	f_v[1] += f_v[5] * v0[3];
	f_v[3] += f_v[5] * v0[1];
	ok     &= std::fabs( f_v[1] - 0.25) <= 1e-10;   // f4_v1
	ok     &= std::fabs( f_v[3] - 0.25) <= 1e-10;   // f4_v3

	// f3( v1 , v2 , v3 )
	f_v[3] += f_v[4] * 1.;
	ok     &= std::fabs( f_v[3] - 1.25) <= 1e-10;   // f3_v3

	// f2( v1 , v2 )
	f_v[2] += f_v[3] / 1.;
	ok     &= std::fabs( f_v[2] - 1.25) <= 1e-10;   // f2_v2

	// f1( v1 )
	f_v[1] += f_v[2] * 1.;
	ok     &= std::fabs( f_v[1] - 1.5 ) <= 1e-10;   // f1_v2

	return ok;
}
/* $$
$end
*/
