Re: [flint-devel] fmpz_poly_evaluate bug in 1.2.2

[Bill H. <goo...@go...>]

Thanks Burcin,

I'll issue a fix for the eval bug as soon as I can. The rest I'll get
back to you about when I find some spare moments. In short, yes, I
think it would be good to include fast versions of these things in
FLINT.

Bill.

2009/3/31 Burcin Erocal <bu...@er...>:
> Hi,
>
> While looking through fmpz_poly.c in 1.2.2, I noticed that the first
> lines of fmpz_poly_evaluate are as follows:
>
> void fmpz_poly_evaluate(fmpz_t output, fmpz_poly_t poly, fmpz_t value)
> {
>   fmpz_t val;
>
>        if ((poly->length == 0) || (value[0] == 0))
>        {
>      output[0] = 0L;
>                return;
>        }
>
> This seems to be a bug, since it always returns 0 if value is 0, when
> it should return the constant coefficient of poly.
>
> I didn't produce a fix, since I wasn't sure if just using
> fmpz_set(output,value) was enough when poly->length == 1 or value == 0.
>
>
> If you wonder why I was reading that file, I need to evaluate
> polynomials in ZZ[x] modulo p as part of some linear algebra routines
> I'm working on. I attached a patch for a function which implements
> evaluation modulo p. Is it possible to include some approximation of
> that in future versions of FLINT?
>
>
> I also need functions to translate (compose with polynomials of degree
> 1) zmod_poly_t's, and fmpz_poly_t's modulo some p. I implemented
> Horner's method in cython to have a reasonably quick way of doing this.
> Do you think it's worth putting these in FLINT?
>
> BTW, in the first part of this article
>
> http://doi.acm.org/10.1145/258726.258745
>
> von zur Gathen and Gerhard measure the performance of different
> algorithms for this task. It might be of interest if we consider making
> this fast in FLINT.
>
>
> Cheers,
> Burcin
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