using gampdf and gamfit

I have found values of gamma distribution using

Y = gampdf(1:40,9,0.5)

Now, from the data I have, I want to estimate the parameters A and B with which I generated gamma distribution values. I mean, I want to get values of A and B near to the 9 and 0.5 respectively.

I have used gamfit function like this:

phat = gamfit(Y)

but I get wrong A and B values. Where is the mistake?

Thank you.

Donatas

[Star Strider]

Consider:

Y = gamrnd(9, .5, 40, 1);

[Donatas]

But why is it not possible to estimate these values using

Y = gampdf(1:40,9,0.5)

I mean, I have a set of points which describes time-concentration curve and I need to fit gamma distribution.

Answer 1

[Amr Hashem]

firstly you have to use:

 Y= gamfit(Data)    % use Data  not Y

then use :

 G= gampdf(X,A,B)
plot(X,G)

the parameters depends on your Data, you can't change them