\(\newcommand{\W}[1]{ \; #1 \; }\) \(\newcommand{\R}[1]{ {\rm #1} }\) \(\newcommand{\B}[1]{ {\bf #1} }\) \(\newcommand{\D}[2]{ \frac{\partial #1}{\partial #2} }\) \(\newcommand{\DD}[3]{ \frac{\partial^2 #1}{\partial #2 \partial #3} }\) \(\newcommand{\Dpow}[2]{ \frac{\partial^{#1}}{\partial {#2}^{#1}} }\) \(\newcommand{\dpow}[2]{ \frac{ {\rm d}^{#1}}{{\rm d}\, {#2}^{#1}} }\)

unary_plus.cpp

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AD Unary Plus Operator: Example and Test

# include <cppad/cppad.hpp>

bool unary_plus(void)
{  bool ok = true;
   using CppAD::AD;


   // domain space vector
   size_t n = 1;
   CPPAD_TESTVECTOR(AD<double>) x(n);
   x[0]      = 3.;

   // 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] = + x[0];

   // create f: x -> y and stop tape recording
   CppAD::ADFun<double> f(x, y);

   // check values
   ok &= ( y[0] == 3. );

   // forward computation of partials w.r.t. x[0]
   CPPAD_TESTVECTOR(double) dx(n);
   CPPAD_TESTVECTOR(double) dy(m);
   size_t p = 1;
   dx[0]    = 1.;
   dy       = f.Forward(p, dx);
   ok      &= ( dy[0] == 1. );   // dy[0] / dx[0]

   // reverse computation of dertivative of y[0]
   CPPAD_TESTVECTOR(double)  w(m);
   CPPAD_TESTVECTOR(double) dw(n);
   w[0] = 1.;
   dw   = f.Reverse(p, w);
   ok &= ( dw[0] == 1. );       // dy[0] / dx[0]

   // use a VecAD<Base>::reference object with unary plus
   CppAD::VecAD<double> v(1);
   AD<double> zero(0);
   v[zero] = x[0];
   AD<double> result = + v[zero];
   ok     &= (result == y[0]);

   return ok;
}