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Re: [Help-gsl] underflow in coulomb_bound.c

From: Ivan Liu
Subject: Re: [Help-gsl] underflow in coulomb_bound.c
Date: Fri, 25 Feb 2005 14:23:24 +0100


I think I found what causes this underflow message. It comes from 


where l > 0 AND r = 0. Looking at the analytical form of the radial
Hydrogenic wavefunction R_nl, in such situations, R_nl is always zero.
Which of course gives underflow error.

So I suggest that, in the underflow check of gsl_sf_hydrogenicR, one
should exclude such situations, and perhaps, which may not be needed,
assigns the result to zero directly.

Ivan Liu

On Fri, 11 Feb 2005 16:06:20 +0000, Brian Gough
<address@hidden> wrote:
> Ivan Liu writes:
>  > My program kept being interrupted by the underflow check when I
>  > compute the coulomb wavefunction with gsl_sf_hydrogenicR. If I turn
>  > of the error handler then the program returns the seemly correct
>  > values.
> Can you send a small standalone program which shows the
> problem--thanks.  (Looking at the function briefly it might be a bug
> in the way underflow is tested).
> --
> Brian Gough
> Network Theory Ltd,
> Commercial support for GSL ---

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