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using gampdf and gamfit

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Donatas
Donatas on 14 Mar 2014
Edited: Amr Hashem on 31 Oct 2015
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
  2 Comments
Star Strider
Star Strider on 14 Mar 2014
Consider:
Y = gamrnd(9, .5, 40, 1);
Donatas
Donatas on 15 Mar 2014
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.

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Answers (1)

Amr Hashem
Amr Hashem on 31 Oct 2015
Edited: Amr Hashem on 31 Oct 2015
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

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