Speex dev - Jul 2009 - A technical question about the speex preprocessor.

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 Is it possible that the comment is out of 
date and the values of Kummer's function used to make the table were 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

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
> 
> 
> _______________________________________________
> Speex-dev mailing list
> Speex-dev at xiph.org
> http://lists.xiph.org/mailman/listinfo/speex-dev
> 
>

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
>>
>>
>> _______________________________________________
>> Speex-dev mailing list
>> Speex-dev at xiph.org
>> http://lists.xiph.org/mailman/listinfo/speex-dev
>>
>>
>>     
>
>
>