What's the difference between gammainc & igamma? Which one should I use to compute incomplete upper gamma function? Which one is scaled??

Incomplete upper gamma function

Answer 1

[John D'Errico]

igamma lives in the stats toolbox. It gives you an upper tail integral.

gammainc lives in MATLAB proper. gammainc is scaled.

The two functions also swap meanings of the arguments. So be careful.

1 - igamma(5,2)/gamma(5)
ans =
        0.0526530173437112

gammainc(2,5)
ans =
        0.0526530173437111