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gammainc
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From: |
Stephen Montgomery-Smith |
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Subject: |
gammainc |
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Date: |
Wed, 05 Dec 2012 19:41:11 -0600 |
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User-agent: |
Mozilla/5.0 (X11; Linux i686; rv:17.0) Gecko/17.0 Thunderbird/17.0 |
On 12/05/2012 06:17 AM, 强哥 wrote:
> Nice to email you.Could you please instruct me that，in Matlab，why
> gammainc（0，0）=0，in detail，how we can get the expression of x^a？I'm expecting
> your reply sincerely.
I presume you are looking at:
http://www.mathworks.com/help/matlab/ref/gammainc.html
If x is small, then in the integrand in the first displayed equation,
e^t is approximately 1. So the integral computes to approximately
x^a / (a gamma(a)) = x^a / gamma(a+1)
Since a is small, gamma(a+1) is approximately gamma(1) = 1.