How to calculate non-centrality of a non central chi square pdf?

Hi everybody, I've got to calculate the non-centrality parameter DELTA of a non central chi square distribution. I know the numer of degrees of freedom V, probability P and value X, so the best MATLAB function I've found is:

X = ncx2inv(P,V,DELTA)

but is it possibile to solve in that form and find DELTA? Or I've to solve the entire non central chi square equation (that is very long and complex)without the help of a MATLAB function?

Thank you for your help! Regards Fabrizio