Function igamma is a numerical inverse of digamma.
igamma
digamma
igamma(v)
igamma(x) is a value u such that digamma(u is approximately x.
igamma(x)
u
digamma(u
x
a numeric in the range [-100000,18]
Peter Ruckdeschel peter.ruckdeschel@uni-oldenburg.de
igamma is vectorized; it is won by spline inversion of a grid; it works well for range [digamma(1e-5);digamma(1e8)] or [-100000,18].
igamma(digamma(c(1e-4,1,20,1e8)))
Run the code above in your browser using DataLab