Re: [Help-gsl] Underflow in gsl_sf_bessel_Jn_array

[Brian Gough]

At Wed, 16 Jul 2008 13:42:44 +0100,
Jonny Taylor wrote:
> 
> Please can somebody advise on using gsl_sf_bessel_Jn_array for small z?
> 
> I need to generate Bessel functions up to some n_max (of order 50) for  
> arbitrary z. I run into problems for small z because the function uses  
> a downward recurrence to populate the array, and suffers underflow for  
> large n.

Could you send a small example program showing the problem to
address@hidden for reference.  Thanks.

> Can anybody suggest a better strategy to take? It seems like this  
> should be a relatively simple thing to ask, but I can't come up with a  
> simple way of achieving it...

It may be possible to modify gsl_sf_bessel_Jn_array to use a scale
factor in the recurrence to avoid underflow.

-- 
Brian Gough

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