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@(@\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}} }@)@
Print During Zero Order Forward Mode: Example and Test
# include <cppad/cppad.hpp>

namespace {
     using std::endl;
     using CppAD::AD;

     // use of PrintFor to check for invalid function arguments
     AD<double> check_log(const AD<double>& y, std::ostream& s_out)
     {     // check AD<double> value during recording
          if( y <= 0 )
               s_out << "check_log: y == " << y << " which is <= 0\n";

          // check double value during zero order forward calculation
          PrintFor(y, "check_log: y == ", y , " which is <= 0\n");

          return log(y);
     }
}

bool print_for(void)
{     bool ok = true;
     using CppAD::PrintFor;
     std::stringstream stream_out;

     // independent variable vector
     size_t n = 1;
     CPPAD_TESTVECTOR(AD<double>) ax(n);
     ax[0] = 1.;         // value of the independent variable during recording
     Independent(ax);

     // A log evaluations that is OK when x[0] = 1 but not when x[0] = 2.
     AD<double> var     = 2. - ax[0];
     AD<double> log_var = check_log(var, stream_out);
     ok &= stream_out.str() == "";

     // dependent variable vector
     size_t m = 1;
     CPPAD_TESTVECTOR(AD<double>) ay(m);
     ay[0]    = log_var;

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

     // zero order forward with x[0] = 2
     CPPAD_TESTVECTOR(double) x(n);
     x[0] = 2.;
     f.Forward(0, x, stream_out);

     std::string string_out = stream_out.str();
     ok &= stream_out.str() == "check_log: y == 0 which is <= 0\n";

     return ok;
}
Input File: example/general/print_for.cpp