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// SPDX-License-Identifier: EPL-2.0 OR GPL-2.0-or-later
// SPDX-FileCopyrightText: Bradley M. Bell <bradbell@seanet.com>
// SPDX-FileContributor: 2003-22 Bradley M. Bell
// ----------------------------------------------------------------------------
/*
{xrst_begin sign.cpp}
Sign Function: Example and Test
###############################
{xrst_literal
// BEGIN C++
// END C++
}
{xrst_end sign.cpp}
*/
// 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++
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