Karim Belabas on Thu, 20 Sep 2012 17:05:38 +0200

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 Re: polresultant disagrees with sage, maxima and magma

```It should have worked, and this was a bug in PARI. All such examples should be
fixed in master HEAD after the following commit:

commit 7079c4f7813c582949dea92a3089bf6a6c532738
Author: Karim Belabas <Karim.Belabas@math.u-bordeaux1.fr>
Date:   Thu Sep 20 16:23:33 2012 +0200

fix: resultant(x,x,y) -> 0 and related problems

Original bug report:
p1=x2*(x3-x4);p2=x2*(x3-2*x4);polresultant(p1,p2,x1) -> 0. Should be 1

Thanks for your report !

K.B.

* Georgi Guninski [2012-09-20 15:35]:
> parisize = 8000000, primelimit = 500509
> ? q1=x2;q2=x2;polresultant(q1,q2,x1)
> %1 = 0
> ? q1=x2;q2=x2;polresultant(q1,q2,x1)
> %2 = 0
> ? p1=y;p2=y;polresultant(p1,p2,x1)
> %3 = 1
>
>
> On Thu, Sep 20, 2012 at 04:09:07PM +0300, Georgi Guninski wrote:
> > I don't claim this is a bug in pari, more like a bug in the
> > mentioned CAS.
> >
> > ? p1=x2*(x3-x4);p2=x2*(x3-2*x4);polresultant(p1,p2,x1)
> > %1 = 0
> >
> > Since p1 and p2 certainly have common roots I expect the resultant
> > w.r.t. x1 (not present in p1 or p2) to be able to vanish.
> >
> > sage, maxima and magma return \$1\$ on the above testcase.
> >
> > Can't see how it can be both ways, which is correct?
--
Karim Belabas, IMB (UMR 5251)  Tel: (+33) (0)5 40 00 26 17
Universite Bordeaux 1          Fax: (+33) (0)5 40 00 69 50
351, cours de la Liberation    http://www.math.u-bordeaux1.fr/~belabas/
F-33405 Talence (France)       http://pari.math.u-bordeaux1.fr/  [PARI/GP]
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