|Bill Allombert on Thu, 20 Sep 2012 15:55:19 +0200|
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|Re: polresultant disagrees with sage, maxima and magma|
On Thu, Sep 20, 2012 at 03:26:57PM +0200, Andreas Enge wrote: > 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. > > As a polynomial in x1, both polynomials are constant and non-zero and so do > not have roots. The correct result should be 1. If x1 has highest priority then indeed the computation is done in Q(x2,x3,x4)[x1] and indeed the result is 1. x1;p1=x2*(x3-x4);p2=x2*(x3-2*x4);polresultant(p1,p2,x1) %1 = 1 Cheers, Bill.