| 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. >