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Re: Request for combinatorial functions

From: Paul Kienzle
Subject: Re: Request for combinatorial functions
Date: Tue, 17 Apr 2007 07:02:37 -0400

On Apr 16, 2007, at 9:00 PM, Jordi Gutierrez Hermoso wrote:

I also see that the current factorial function in the 'Forge isn't
simply an alias for the gamma function, which it really should

More correctly, use round(gamma(x+1))

This should be fixed. Looks like the factorial function was
written a long time ago, perhaps before the gamma function was

No, there was just no compelling reason to use it.

I played around a bit to see if gamma(n+1) is any more accurate
than prod(1:n) as compared to exp(sum(log(1:n))) and found that
no it is not.  Also, speed/space is not an issue since the
function is small and cheap in either case.

That said, I'm submitting the gamma version to address@hidden since
I've thrown in a few test cases.

- Paul

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