# include <cppad/cppad.hpp>
bool atan2(void)
{ bool ok = true;
using CppAD::AD;
using CppAD::NearEqual;
double eps99 = 99.0 * std::numeric_limits<double>::epsilon();
// 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);
// a temporary value
AD<double> sin_of_x0 = CppAD::sin(x[0]);
AD<double> cos_of_x0 = CppAD::cos(x[0]);
// range space vector
size_t m = 1;
CPPAD_TESTVECTOR(AD<double>) y(m);
y[0] = CppAD::atan2(sin_of_x0, cos_of_x0);
// create f: x -> y and stop tape recording
CppAD::ADFun<double> f(x, y);
// check value
ok &= NearEqual(y[0] , x0, eps99, eps99);
// 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);
ok &= NearEqual(dy[0], 1., eps99, eps99);
// 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], 1., eps99, eps99);
// use a VecAD<Base>::reference object with atan2
CppAD::VecAD<double> v(2);
AD<double> zero(0);
AD<double> one(1);
v[zero] = sin_of_x0;
v[one] = cos_of_x0;
AD<double> result = CppAD::atan2(v[zero], v[one]);
ok &= NearEqual(result, x0, eps99, eps99);
return ok;
}