Re: Libpari Function Somme

[Bill Allombert <Bill.Allombert@math.u-bordeaux1.fr>]

On Mon, Sep 17, 2007 at 10:30:24AM -0700, Thomas D. Dean wrote:
> I have a problem using the libpari function, somme.
> 
> Help on sum shows:
> 
> The library syntax is somme(entree *ep, GEN a, GEN b, char *expr, GEN
> x).  This is to be used as follows: ep represents the dummy variable
> used in the expression expr
> 
>    /* compute a^2 + ... + b^2 */
>    {
>      /* define the dummy variable "i" */
>      entree *ep = is_entry("i");
>      /* sum for a <= i <= b */
>      return somme(ep, a, b, "i^2", gen_0);
>    }
>    
> However, my code
> 
> entree *ep = is_entry("i");
> s = somme(ep, gen_1, n, "i^2", gen_0);
> 
> produces the fault:
> 
>   ***   segmentation fault: bug in PARI or calling program.
>   ***   Error in the PARI system. End of program.

Yes, you need to use fetch_named_var("i") because
is_entry("i") fails if the variable "i" does not already exist,
which is the case here.

But I strongly suggest to avoid using 'somme' here, because it will not
work with PARI/GP 2.4.

Cheers,
Bill