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Thread Subject:
inverse gamma function

Subject: inverse gamma function

From: Dipen Bepari

Date: 7 Jul, 2011 11:31:10

Message: 1 of 3

i want to solve the equation given bellow-
> f=incomplete gamma function(u,x);
> f=.0001;
> u=5;
> now i need to find out x.
please help me by solving x

Subject: inverse gamma function

From: Alan Weiss

Date: 7 Jul, 2011 12:02:05

Message: 2 of 3

On 7/7/2011 7:31 AM, Dipen Bepari wrote:
> i want to solve the equation given bellow-
>> f=incomplete gamma function(u,x);
>> f=.0001;
>> u=5;
>> now i need to find out x.
> please help me by solving x

Take a look at fzero. Your equation would be something like @(x)f(5,x)-.0001

Alan Weiss
MATLAB mathematical toolbox documentation

Subject: inverse gamma function

From: Torsten

Date: 7 Jul, 2011 12:28:15

Message: 3 of 3

On 7 Jul., 13:31, "Dipen Bepari" <dipen.jge...@gmail.com> wrote:
> i want to solve the equation given bellow->   f=incomplete gamma function(u,x);
> > f=.0001;
> > u=5;
> > now i need to find out x.
>
> please help me by solving x

If f=gammainc(x,u,'lower'), then x=gammaincinv(f,u,'lower').
If f=gammainc(x,u,'upper'), then x=gammaincinv(f,u,'upper').

So

f=0.0001;
u=5;
x=gammaincinv(f,u,'lower');

will give you x for which gammainc(x,5,'lower')=0.0001

whereas

f=0.0001;
u=5;
x=gammaincinv(f,u,'upper');

will give you x for which gammainc(x,5,'upper')=0.0001.


Best wishes
Torsten.

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