Dear list, Is there an incomplete gamma function in R that can take negative arguments? If not, pointers to its implementation will be greatly appreciated. I know the 'Igamma' function in 'zipfR' package. However, Igamma(a,x) only takes positive x. (When x is negative, this function should return a value that is complex. Matlab function 'gammainc' can handle negative arguments. But it is an internal Matlab function, so I don't get to see how it is done.) Thanks! X.W.