#include struct fun { typedef double result_type; typedef double argument_type; // gives the coefficients of the matrix (function F of the documentation) double operator()(double x, double y) const { return (x - y); } }; int main() { fun f; int init_size = 100; // maximum size of the matrix before a resize // creation of a class det_manip triqs::det_manip::det_manip D(f, init_size); // the initial matrix is empty: std::cout << std::endl << "After construction: D.matrix()=" << D.matrix() << std::endl << std::endl; }