Re: Making some minor contributions to GSL

[Gerard Jungman <jungman at lanl dot gov>]

On Tue, 2004-01-13 at 11:17, linas@austin.ibm.com wrote:
> 
> I have some code that might be appropriate for inclusion with GSL,
> and was curious to gauge interest, and understand the hurdles 
> involved.  
> 
> Polygamma functions, Abramowitz & Stegun chapter 6.4 -- these
> are derivatives of the gamma (factorial) function.   The algo
> I have is fairly straightforward ... and is accurate to about
> 1e-14 or so for "small" orders and arguments.  (The "multiplication
> theorm" breaks down above order 30 or 40 or so, i.e. for arguments
> greater than a 100 or 200 or so. I'm not sure why.)

I have never made a study of robustness of the GSL
implementation, in gsl_sf_psi_n(). There are only
the test cases in specfunc/test_sf.c. Is there
a specific deficiency in the GSL implementation?

If you have some test cases that break it, please
send them so I can check it out. If you have code
that can plug a hole in the current implementation,
then that would be greatly appreciated.

Thanks,
G. Jungman