[R] Incomplete Gamma function

[poolloopus at yahoo.com]

Hello 

I am trying to evaluate an Incomplete gamma function
in R. Library Zipfr gives the Igamma function. From
Mathematica, I have:

"Gamma[a, z] is the incomplete gamma function."

In[16]: Gamma[9,11.1]
Out[16]: 9000.5

Trying the same in R, I get

> Igamma(9,11.1)
[1] 31319.5
OR
> Igamma(11.1,9)
[1] 1300998

I know I have to understand the theory and the math
behind it rather than just ask for help, but while I
am trying to do that (and only taking baby steps, I
must admit), I was hoping someone could help me out.

Regard

Kris.


       
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