/* $Id: sqrt.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
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 sqrt.cpp$$
$spell
sqrt
$$
$section The AD sqrt Function: Example and Test$$
$index sqrt, AD example$$
$index example, AD sqrt$$
$index test, AD sqrt$$
$code
$verbatim%example/sqrt.cpp%0%// BEGIN C++%// END C++%1%$$
$$
$end
*/
// BEGIN C++
# include <cppad/cppad.hpp>
# include <cmath>
bool Sqrt(void)
{ bool ok = true;
using CppAD::AD;
using CppAD::NearEqual;
// domain space vector
size_t n = 1;
double x0 = 0.5;
CPPAD_TESTVECTOR(AD<double>) x(n);
x[0] = x0;
// declare independent variables and start tape recording
CppAD::Independent(x);
// range space vector
size_t m = 1;
CPPAD_TESTVECTOR(AD<double>) y(m);
y[0] = CppAD::sqrt(x[0]);
// create f: x -> y and stop tape recording
CppAD::ADFun<double> f(x, y);
// check value
double check = std::sqrt(x0);
ok &= NearEqual(y[0] , check, 1e-10 , 1e-10);
// forward computation of first partial w.r.t. x[0]
CPPAD_TESTVECTOR(double) dx(n);
CPPAD_TESTVECTOR(double) dy(m);
dx[0] = 1.;
dy = f.Forward(1, dx);
check = 1. / (2. * std::sqrt(x0) );
ok &= NearEqual(dy[0], check, 1e-10, 1e-10);
// reverse computation of derivative of y[0]
CPPAD_TESTVECTOR(double) w(m);
CPPAD_TESTVECTOR(double) dw(n);
w[0] = 1.;
dw = f.Reverse(1, w);
ok &= NearEqual(dw[0], check, 1e-10, 1e-10);
// use a VecAD<Base>::reference object with sqrt
CppAD::VecAD<double> v(1);
AD<double> zero(0);
v[zero] = x0;
AD<double> result = CppAD::sqrt(v[zero]);
check = std::sqrt(x0);
ok &= NearEqual(result, check, 1e-10, 1e-10);
return ok;
}
// END C++