Inverse Digamma Function (Matlab)

This MATLAB function computes the inverse of the Digamma (or Psi) function. The digamma function is the derivative of the natural log of the gamma function. More information can be found at Wikipedia or Mathworld.

The inverse of this function is the Y > 0, given X, such that digamma(Y) = X. The algorithm is taken more or less directly from code written by Paul Fackler.