Re: [Help-gsl] gsl_sum (potential division by zero?)

[Michel Van den Bergh]

Hi Brian,

I now understand that the code is consistent with the philosophy behind gsl.
Thanks for the wonderful package.

Michel


Brian Gough wrote:

> At Sun, 24 Dec 2006 13:35:14 +0100,
> Michel Van den Bergh wrote:
>  
>
> > I was looking at the code for gsl_sum. I have not completely
> > understood it yet, but I noticed that whereas levin_utrunc.c
> > explicitly tests for terms that are zero, this is not the case for
> > levin_u.c. As one divides by such terms, it seems that one may
> > potentially divide by zero this way. Am I wrong?
> >    
>
> Hello,
>
> Thanks for your email.  I think the original code that the routine was
> translated from assumes that all terms passed in are non-zero since
> any others would not contribute to the sum.
>
>  
>
> > The documentation does not seem to mention that terms should be
> > different from zero.
> >    
>
> Yes, I will add a note about that.
>
>  
>
> > I am not a numerical analyst (IANANA) but it seems to me that even in
> > levin_utrunc.c no motivation is given for discarding zero terms.
> > Wouldn't it be more natural to add a bit of noise to the remainder
> > estimates to reduce the risk of division by zero? 
> >    
>
> Generally in GSL we just implement what is published in the
> literature, so far I have not seen any newer algorithms published.
>
>