John Cremona on Thu, 20 Sep 2012 18:05:16 +0200

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 Re: polresultant disagrees with sage, maxima and magma

```On 20 September 2012 16:56, Bill Allombert
<Bill.Allombert@math.u-bordeaux1.fr> wrote:
> On Thu, Sep 20, 2012 at 03:19:52PM +0100, John Cremona wrote:
>>
>> I don't think this is a good enough answer (sorry, Bill!).    I know
>> that there are reasons for pari's variable priorities, and I have
>> personally been entertained by hem for many years,  but  if
>> "polresultant(p1,p2,x1)" is to correspond to any mathematically
>> correct resultant function then it has to be independent of that
>> (invisible) priority.
>
> I agree with you, I was just pointing out the discrepancy!

Sure.

>
> On Thu, Sep 20, 2012 at 05:05:25PM +0200, Karim Belabas wrote:
>> 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
>
> Should I backport it to pari 2.5.3 ?
>

If it is simple to do, and if you are doing the same for other minor
bigfixes, and if 2.6.0 is not due out soon, then yes.  For myself, I
am already using pre-releases of 2.6.0 anyway (and have been for 8
months) on account of the wonderful ellheegner function!

John

> Cheers,
> Bill.
>

```