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From: "Mohammad Monfared" <gohardoust@gmail.com>
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Subject: Re: fitting a Gamma cdf to my data
Date: Thu, 9 Oct 2008 21:33:01 +0000 (UTC)
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"aasim Azooz" <aasimazooz@yahoo.com> wrote in message <gcl2c9$i8$1@fred.mathworks.com>...
> 
> Dear Reza
> Can you tell me what do you mean by cdf? is it a Gamma function of some type I may help you
> Aasim Azooz

Hi,
cdf is for Cumulative Density Function. 
my data are about soil particle size and their fraction in a sample. for a soil sample, I have:

p_size=[2 50 106 250 500 1000 2000]
p_fraction=[0.0300 0.1700 0.2790 0.7350 0.9210 0.9940 1.0020]

which says e.g. 27.90% of our soil particles size is less than 106. I don't know how to prepare them for 'gamfit' function (if possible).
as a graph:
stairs([0 p_size],[p_fraction 1.0020])

And thanks Tom, for your explanatory answer! 
thanks again,
Reza,