Re: tolerance in binopdf.m

[Ben Abbott]

On Sep 21, 2011, at 1:59 AM, Jordi Gutiérrez Hermoso wrote:

> Just for fun, I asked someone to run this program on a Macintosh:
> 
>    #include <stdio.h>
>    #include <math.h>
> 
>    int main()
>    {
>      printf("%0.100f\n",lgamma(3.0));
>    }
> 
> It turns out it does run, i.e. it does have an lgamma implementation.
> However, the exact value it outputs is 390207173010335/2^49, while on
> my Debian system, the exact value it outputs is
> 31216573840826795/2^52. It seems that somewhere along the way, 3 bits
> of precision were lost on the Macintosh.
> 
> So I don't think there's anything we can do other than increase the
> tolerance by 3 bits to account for this. We already increase tolerance
> slightly for other systems for other tests.
> 
> HTH,
> - Jordi G. H.

Thanks for all the quick replies. From config.log I see ...

| #define HAVE_LGAMMA 1
| #define HAVE_LGAMMAF 1
| #define HAVE_LGAMMA_R 1
| #define HAVE_LGAMMAF_R 1

Thus, it looks to me as if Apple has a different implementation of lgamma (?).

As this is not a bug in Octave, I'm inclined to add a tolerance for MaOS.

However, I'm curious about what Apple did.

I'm using Xcode 4.1. The sources are below.

        http://www.opensource.apple.com/

Does anyone have an idea of where to look to find the sources for lgamma?

Ben