[R] incomplete gamma function with negative arguments

[Ximing Wu]

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.