/* $Id: sign.cpp 2506 2012-10-24 19:36:49Z bradbell $ */
/* --------------------------------------------------------------------------
CppAD: C++ Algorithmic Differentiation: Copyright (C) 2003-12 Bradley M. Bell

CppAD is distributed under multiple licenses. This distribution is under
the terms of the 
                    Eclipse Public License Version 1.0.

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 sign.cpp$$
$spell
$$

$section Sign Function: Example and Test$$

$index sign, example$$
$index example, sign$$
$index test, sign$$

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

$end
*/
// BEGIN C++

# include <cppad/cppad.hpp>

bool sign(void)
{	bool ok = true;

	using CppAD::AD;
	using CppAD::NearEqual;

	// create f: x -> y where f(x) = sign(x)
	size_t n = 1;
	size_t m = 1;
	CPPAD_TESTVECTOR(AD<double>) ax(n), ay(m);
	ax[0]     = 0.;
	CppAD::Independent(ax);
	ay[0]     = sign(ax[0]);
	CppAD::ADFun<double> f(ax, ay);

	// check value during recording
	ok &= (ay[0] == 0.);

	// use f(x) to evaluate the sign function and its derivatives
	CPPAD_TESTVECTOR(double) x(n), y(m), dx(n), dy(m), w(m), dw(n);
	dx[0] = 1.;
	w[0] = 1.; 
	//
	x[0]  = 2.;
	y     = f.Forward(0, x);
	ok   &= (y[0] == 1.);
	dy    = f.Forward(1, dx);
	ok   &= (dy[0] == 0.);
	dw   = f.Reverse(1, w);
	ok  &= (dw[0] == 0.);
	//
	x[0]  = 0.;
	y     = f.Forward(0, x);
	ok   &= (y[0] == 0.);
	dy    = f.Forward(1, dx);
	ok   &= (dy[0] == 0.);
	dw   = f.Reverse(1, w);
	ok  &= (dw[0] == 0.);
	//
	x[0]  = -2.;
	y     = f.Forward(0, x);
	ok   &= (y[0] == -1.);
	dy    = f.Forward(1, dx);
	ok   &= (dy[0] == 0.);
	dw   = f.Reverse(1, w);
	ok  &= (dw[0] == 0.);

	// use a VecAD<Base>::reference object with sign
	CppAD::VecAD<double> v(1);
	AD<double> zero(0);
	v[zero]           = 2.;
	AD<double> result = sign(v[zero]);
	ok   &= (result == 1.);

	return ok;
}

// END C++
