Hello, thanks but I resolve the former problem...besides I have a new onenow the expresion ex that is well casted from the string is not well transformed into a derivative with diff         parser reader;         e = reader(ramaPrim[i]);         cout<<"ex="<<e<<" diff:"<<e.diff(r).subs(r==Pi)<< " i="<<i<<endl; e is well printed and is a function of r but its derivative is cero!What is happening hereThanks