[Speex-dev] A technical question about the speex preprocessor.

Jean-Marc Valin
Wed, 22 Jul 2009 15:44:23 -0000

OK, so the problem is that the table you see does not match the definition?
y = gamma(1.25)^2 * M(-.25;1;-x) / sqrt(x)
Note that the table data has an interval of .5 for the x axis.

How far are your results from the data in the table?

Cheers,

   Jean-Marc

Quoting John Ridges <jridges at masque.com>:

> Thanks for the confirmation  Jean-Marc. I kind of suspected from the
> comments that it was the confluent hypergoemetric function, which I was
> trying to evaluate using Kummer's equation, namely:
>
> M(a;b;x) is the sum from n=0 to infinity of (a)n*x^n / (b)n*n!
> where (a)n = a(a+1)(a+2) ... (a+n-1)
>
> But when I use Kummer's equation, I don't get the values in the
> "hypergeom_gain" table. Did you use a different solution to the
> confluent hypergoemetric function when you created the table?
>
> John Ridges
>
>
> Jean-Marc Valin wrote:
> > Hi John,
> >
> > M(;;) is the confluent hypergeometric function.
> >
> > 	Jean-Marc
> >
> > John Ridges a ?crit :
> >
> >> Hi,
> >>
> >> I've been trying to re-create the table in the function
"hypergeom_gain"
> >> in preprocess.c, and I just simply can't get the same values.
I get the
> >> same value for the first element, so I know I'm computing
gamma(1.25)^2
> >> correctly, but I can't get the same numbers for M(-.25;1;-x),
which I
> >> assume is Kummer's function. Is it possible that the comment
is out of
> >> date and the values of Kummer's function used to make the
table were
> >> different? Any help would be greatly appreciated.
> >>
> >> John Ridges
> >>
> >>
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> >> http://lists.xiph.org/mailman/listinfo/speex-dev
> >>
> >>
> >>
> >
> >
> >
>
>
>