# 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;
}