Hi,

 I need help with the incomplete gamma function with real but negative
fraction value of x. I found the M_Igamma(x,a)in Meron
Library(http://www.astro.washington.edu/deutsch/idl/htmlhelp/slibrary23.html)
which works for both real and complex  x. However, I notice that
M_Igamma (x,a),  for a real but negative fraction value of x, give
only the real part. If any body knows how to deal with this problem
please help me. You might use the following arguments: x=-0.069, a=
2.2.  Thank you very much for your help in advance.

Dag

In article <162586e3.0310130746.5997d5bf@posting.google.com>, biomedthesis2002@yahoo.com (New2IDL) writes:
>Hi,
>
> I need help with the incomplete gamma function with real but negative
>fraction value of x. I found the M_Igamma(x,a)in Meron
>Library(http://www.astro.washington.edu/deutsch/idl/htmlhelp/slibrary23.html)
>which works for both real and complex  x. However, I notice that
>M_Igamma (x,a),  for a real but negative fraction value of x, give
>only the real part. If any body knows how to deal with this problem
>please help me. You might use the following arguments: x=-0.069, a=
>2.2.  Thank you very much for your help in advance.

Well, I can actually help you on this one.  First, though, I suggest 
you use the updated version of the routine (called Igamma_mm), you can 
find it in my library on the RSI users contribution page.

Now, as for your question, Igamma_mm returns an output which is of the 
same numerical type as x (no lower than float, though).  So, if x is real, 
so will be the output.  If you want a full complex output, you need 
complex input.  See below:

IDL> print, igamma_mm(-0.069,2.2)
  0.000976233
IDL> print, igamma_mm(complex(-0.069),2.2)
(  0.000976233,  0.000709275)

Hope this helps.

Mati Meron                      | "When you argue with a fool,
meron@cars.uchicago.edu         |  chances are he is doing just the same"