Incomplete multivariate factorization

[jdemeyer]

With sage-6.4.beta6, the following polynomial factorization gives a reducible factor (-a^2 + b^2):

sage: R.<z,a,b> = PolynomialRing(QQ)
sage: N = -a^4*z^8 + 2*a^2*b^2*z^8 - b^4*z^8 - 16*a^3*b*z^7 + 16*a*b^3*z^7 + 28*a^4*z^6 - 56*a^2*b^2*z^6 + 28*b^4*z^6 + 112*a^3*b*z^5 - 112*a*b^3*z^5 - 70*a^4*z^4 + 140*a^2*b^2*z^4 - 70*b^4*z^4 - 112*a^3*b*z^3 + 112*a*b^3*z^3 + 28*a^4*z^2 - 56*a^2*b^2*z^2 + 28*b^4*z^2 + 16*a^3*b*z - 16*a*b^3*z - a^4 + 2*a^2*b^2 - b^4
sage: N.factor()
(-1) * (-a^2 + b^2) * (-z^4*a + z^4*b - 4*z^3*a - 4*z^3*b + 6*z^2*a - 6*z^2*b + 4*z*a + 4*z*b - a + b) * (z^4*a + z^4*b - 4*z^3*a + 4*z^3*b - 6*z^2*a - 6*z^2*b + 4*z*a - 4*z*b + a + b)

This is fixed by #17254.

Upstream: Completely fixed; Fix reported upstream

CC: @sagetrac-jakobkroeker

Component: factorization

Keywords: singular

Author: Frédéric Chapoton

Branch/Commit: 8ce76ba

Reviewer: Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/17251

[jdemeyer]

Changed keywords from none to singular

[jdemeyer]

Upstream: Completely fixed; Fix reported upstream

[jdemeyer]

Dependencies: #17254

[sagetrac-jakobkroeker]

comment:5

Next: add a test.

[fchapoton]

New commits:

8ce76ba

trac 17251 adding a doctest for factorisation of polynomials

[fchapoton]

Commit: 8ce76ba

[fchapoton]

Branch: u/chapoton/17251

[fchapoton]

Changed dependencies from #17254 to none

[fchapoton]

Author: Frédéric Chapoton

[tscrim]

Reviewer: Travis Scrimshaw

[tscrim]

comment:8

LGTM.

[vbraun]

Changed branch from u/chapoton/17251 to 8ce76ba