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Thread Subject:
inverse gamma function

Subject: inverse gamma function

From: Dipen Bepari

Date: 7 Jul, 2011 09:35:11

Message: 1 of 5

i like to solve the equation given bellow-
  f=incomplete gamma function(u,x);
f=.0001;
u=5;
now ilike to find out x.

i have tried like-
 x=gammaincinv((1-f),u,'lower')

Subject: inverse gamma function

From: Torsten

Date: 7 Jul, 2011 09:49:33

Message: 2 of 5

On 7 Jul., 11:35, "Dipen Bepari" <dipen.jge...@gmail.com> wrote:
> i like to solve the equation given bellow-
>   f=incomplete gamma function(u,x);
> f=.0001;
> u=5;
> now ilike to find out x.
>
> i have tried like-
>  x=gammaincinv((1-f),u,'lower')

You can easily check whether you are right by
calculating hereafter
y=gammainc(x,u)
If y=f, you are done (assuming you use the same definition for the
gammainc function as MATLAB does).

Best wishes
Torsten.

Subject: inverse gamma function

From: Roger Stafford

Date: 7 Jul, 2011 23:16:10

Message: 3 of 5

"Dipen Bepari" <dipen.jgec04@gmail.com> wrote in message <iv3ukf$and$1@newscl01ah.mathworks.com>...
> i like to solve the equation given bellow-
> f=incomplete gamma function(u,x);
> f=.0001;
> u=5;
> now ilike to find out x.
>
> i have tried like-
> x=gammaincinv((1-f),u,'lower')
- - - - - - - - - - - -
  You are attempting to find the inverse with respect to the second argument - the gamma function parameter - of gammainc. However, the function gammaincinv finds the inverse with respect to the first argument - the limit of integration - which is a very different problem.

  Why don't you try using fzero on it?

Roger Stafford

Subject: inverse gamma function

From: pramod.7588@gmail.com

Date: 4 Oct, 2013 20:50:59

Message: 4 of 5

Does anybody has code for it. Even algorithm to find it is sufficient.

Subject: inverse gamma function

From: Steven Lord

Date: 7 Oct, 2013 14:52:52

Message: 5 of 5


<pramod.7588@gmail.com> wrote in message
news:5d226621-46b7-4a30-a36a-5c6bc855f3ab@googlegroups.com...
> Does anybody has code for it. Even algorithm to find it is sufficient.

Have you tried the approach Roger suggested a little over two years ago in
the previous message in this thread?

http://www.mathworks.com/matlabcentral/newsreader/view_thread/310187#912124

--
Steve Lord
slord@mathworks.com
To contact Technical Support use the Contact Us link on
http://www.mathworks.com

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