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

var2par.cpp

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Convert a Variable or Dynamic Parameter a Constant: Example and Test

# include <cppad/cppad.hpp>


bool Var2Par(void)
{  bool ok = true;
   using CppAD::AD;
   using CppAD::Value;
   using CppAD::Var2Par;

   // independent variables
   size_t nx = 2;
   CPPAD_TESTVECTOR(AD<double>) ax(nx);
   ax[0] = 3.;
   ax[1] = 4.;

   // independent dynamic paramers
   size_t np = 1;
   CPPAD_TESTVECTOR(AD<double>) ap(np);
   ap[0] = 5.;

   // declare independent variables and dynamic parameters
   CppAD::Independent(ax, ap);

   // range space vector
   size_t ny = 2;
   CPPAD_TESTVECTOR(AD<double>) ay(ny);
   ay[0] = - ax[1] * Var2Par(ax[0]);    // same as ay[0] = -ax[1] * 3.;
   ay[1] = - ax[1] * Var2Par(ap[0]);    // same as ay[1] = -ax[1] * 5.;

   // Must convert these objects to constants before calling Value
   ok &= ( Value( Var2Par(ax[0]) ) == 3. );
   ok &= ( Value( Var2Par(ax[1]) ) == 4. );
   ok &= ( Value( Var2Par(ap[0]) ) == 5. );
   ok &= ( Value( Var2Par(ay[0]) ) == -12. );
   ok &= ( Value( Var2Par(ay[1]) ) == -20. );

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

   // All AD object are currently constants
   ok &= (Value(ax[0]) ==  3.);
   ok &= (Value(ax[1]) ==  4.);
   ok &= (Value(ap[0]) ==  5.);
   ok &= (Value(ay[0]) == -12.);
   ok &= (Value(ay[1]) == -20.);

   // evaluate zero order forward mode
   // (note that the only real variable in this recording is x[1])
   CPPAD_TESTVECTOR(double) x(nx), p(np), y(ny);
   x[0] = 6.;
   x[1] = 7.;
   p[0] = 8.;
   f.new_dynamic(p);
   y    = f.Forward(0, x);
   ok  &= y[0] == - x[1] * 3.0;
   ok  &= y[1] == - x[1] * 5.0;

   return ok;
}