toy.raymond at gmail.com
Mon Nov 30 20:28:27 CST 2009
Dieter Kaiser wrote:
> Am Montag, den 30.11.2009, 19:03 -0500 schrieb Raymond Toy:
>> Current CVS says gamma_incomplete(1/2,0) is sqrt(%pi)/2. But the help
>> for gamma_incomplete says gamma_incomplete(a,z) =
>> integrate(exp(-t)*t^(a-1),t,0,z). (This matches A&S 6.5.2.)
>> So from the documentation, I would expect the integral to be 0.
>> Which is correct? Since A&S is our reference, I think the current value
>> is incorrect and we should return 0.
> Sorry, but I think the documentation is wrong. The problem is that the
> Incomplete Gamma function and the lower Incomplete Gamma function are
> easy to mix up. I think these are the defintions (e.g. wolfram.com)
> Incomplete Gamma functions:
> gamma_incomplete(a,z) = integrate(exp(-t)*t^(a-1),t,z,inf)
Heh. That would explain why limit(gamma_incomplete(a,z),z,inf) is zero.
Let's fix the documentation then.
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