int f2cad::dscal_(integer *n, doublereal *da, doublereal *dx, integer *incx);
This is a simple example using Fadbad and the libf2cadFadbad.a library routine dscal to compute the function   $f(a) = a \left( \begin{array}{c} 1 \\ 2 \end{array} \right)$  We check that the derivative of this function, calculated using the Fadbad, satisfies   $f^{(1)} (a) = \left( \begin{array}{c} 1 \\ 2 \end{array} \right)$   // standard input output library # include <iostream> // f2cad set up for F<double> # define F2CAD_USE_FADBAD // prototype for dscal # include <f2cad/dscal.hpp> int main(void) { // independent variables doublereal a[1]; // vector of independent variables a[0] = 5.; // value of independent variables a[0].diff(0, 1); // declare independent variables // create data structure expected by dscal integer m = 2; doublereal f[2]; f[0] = 1.; f[1] = 2.; integer incf = 1; // set f = a * f f2cad::dscal_(&m, a, f, &incf ); // print results std::cout << "f(a) = a * (1, 2)^T" << std::endl; std::cout << "f'(a) = (" << f[0].d(0) << ", " << f[1].d(0) << ")^T" << std::endl; // return value not significant if( f[0].d(0) != 1. || f[1].d(0) != 2. ) return 1; // error return 0; // no error }