[GiNaC-list] psi (digamma) solving

f=psi(x/2)==0;

Hi All, I'm trying to solve function that contains a call to psi (digamma) but my call to fsolve fails every time, ie: psi(1/2*x)==0

fsolve(f,x,2.7,3.1); fsolve(): function does not evaluate numerically

but I'd expect the result to be x~=2.923... Am I missing something here? Thanks for your help! Cheers, Matej