Karim BELABAS on Wed, 4 Dec 2002 22:27:15 +0100 (MET)


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Re: regression in ZX_resultant_all()


On Wed, 4 Dec 2002, Igor Schein wrote:
> it can be reproduced by the following:
>
> ? polgalois(subst(x^8-n*x^6+(2*n+14)*x^4-n*x^2+1,n,600!))
> [40320, -1, 50]
>
> It stopped working Nov 6, 2002.  ZX_resultant_all() returns a number
> which is not a square, and galoisbig() thinks the group is ODD.

Precision error [ the algebraic resultant bound is huge: we compute a
floating point approximation to the resultant, and it turns out to be
0.E4000, with no digit of accuracy left ].

It should be fixed now.

    Karim.
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Karim Belabas                    Tel: (+33) (0)1 69 15 57 48
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Université Paris-Sud             Email: Karim.Belabas@math.u-psud.fr
F-91405 Orsay (France)           http://www.math.u-psud.fr/~belabas/
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