It is trying to use a dvar_matrix constructor to print out the object. The constructor is declared in the header fvar.hpp, but I guess never implemented. Probably do it yourself with something like init_bounded_vector_vector dFt(1,nsp,1,nFt,-5,5,phase); matrix M(1,nsp) LOC_CALCS for (int i=1;i<=n;i++) { M(i)=dFt(i); } and use M in your code.