Re: [Bug-gsl] gsl_sf_hyperg_1F1

[Brian Gough]

At Thu, 21 Jan 2010 16:12:45 +0100,
Lorenzo Moneta wrote:
>   gsl_sf_hyperg_1F1(-1.5, 1.5, - 99.9)  returns the correct value of  
> 4.55768964383819423e+02
> while gsl_sf_hyperg_1F1(-1.5, 1.5, -100.) returns -1.13760e+20 when the 
> correct value is 456.44  (from Mathematica)
> I think the Kummer formula (    1F1(a,b,x) = exp(-x) * 1F1(b-a,b,-x) could be 
> used for larger value of |x| ( at least works for |x| = 700), while 
> the current cut-off is for |x| < 100. 

Thanks for the suggestion, Lorenzo.  I've added a test case for your
example and extended the range for using the Kummer formula up to
|x|<2*GSL_LOG_DBL_MAX (|x| < ~1400) -- so it is computed correctly
now.

-- 
Brian Gough

GNU Scientific Library -
http://www.gnu.org/software/gsl/