$\newcommand{\W}[1]{ \; #1 \; } \newcommand{\R}[1]{ {\rm #1} } \newcommand{\B}[1]{ {\bf #1} } \newcommand{\D}[2]{ \frac{\partial #1}{\partial #2} } \newcommand{\DD}[3]{ \frac{\partial^2 #1}{\partial #2 \partial #3} } \newcommand{\Dpow}[2]{ \frac{\partial^{#1}}{\partial {#2}^{#1}} } \newcommand{\dpow}[2]{ \frac{ {\rm d}^{#1}}{{\rm d}\, {#2}^{#1}} }$
 # include <cppad/cppad.hpp> bool Var2Par(void) { bool ok = true; using CppAD::AD; using CppAD::Value; using CppAD::Var2Par; // domain space vector size_t n = 2; CPPAD_TESTVECTOR(AD<double>) x(n); x[0] = 3.; x[1] = 4.; // 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[1] * Var2Par(x[0]); // same as y[0] = -x[1] * 3.; // cannot call Value(x[j]) or Value(y[0]) here (currently variables) ok &= ( Value( Var2Par(x[0]) ) == 3. ); ok &= ( Value( Var2Par(x[1]) ) == 4. ); ok &= ( Value( Var2Par(y[0]) ) == -12. ); // create f: x -> y and stop tape recording CppAD::ADFun<double> f(x, y); // can call Value(x[j]) or Value(y[0]) here (currently parameters) ok &= (Value(x[0]) == 3.); ok &= (Value(x[1]) == 4.); ok &= (Value(y[0]) == -12.); // evaluate derivative of y w.r.t x CPPAD_TESTVECTOR(double) w(m); CPPAD_TESTVECTOR(double) dw(n); w[0] = 1.; dw = f.Reverse(1, w); ok &= (dw[0] == 0.); // derivative of y[0] w.r.t x[0] is zero ok &= (dw[1] == -3.); // derivative of y[0] w.r.t x[1] is 3 return ok; }