[R] Incomplete Gamma function

[Robin Hankin]

Hi Kris


lgamma() gives the log of the gamma function.

You need gamma_inc() of the gsl package, a wrapper for the
GSL library:

 > gamma_inc(9,11.1)
[1] 9000.501
 >

HTH

rksh





On 31 Aug 2007, at 00:29, poolloopus at yahoo.com wrote:

> 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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--
Robin Hankin
Uncertainty Analyst
National Oceanography Centre, Southampton
European Way, Southampton SO14 3ZH, UK
  tel  023-8059-7743