Opened 6 years ago

Closed 3 years ago

# Incomplete multivariate factorization

Reported by: Owned by: jdemeyer critical sage-8.2 factorization singular jakobkroeker Frédéric Chapoton Travis Scrimshaw Completely fixed; Fix reported upstream 8ce76ba (Commits) 8ce76ba086323151cbbd4227d51340749cb7ff2f

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.

### comment:2 Changed 6 years ago by jdemeyer

• Description modified (diff)

### comment:3 Changed 6 years ago by jdemeyer

• Description modified (diff)
• Report Upstream changed from N/A to Completely fixed; Fix reported upstream

### comment:4 Changed 6 years ago by jdemeyer

• Dependencies set to #17254

### comment:6 Changed 3 years ago by chapoton

• Authors set to Frédéric Chapoton
• Branch set to u/chapoton/17251
• Commit set to 8ce76ba086323151cbbd4227d51340749cb7ff2f
• Dependencies #17254 deleted
• Status changed from new to needs_review

New commits:

 ​8ce76ba `trac 17251 adding a doctest for factorisation of polynomials`

### comment:7 Changed 3 years ago by chapoton

• Milestone changed from sage-6.4 to sage-8.2

### comment:8 Changed 3 years ago by tscrim

• Reviewers set to Travis Scrimshaw
• Status changed from needs_review to positive_review

LGTM.

### comment:9 Changed 3 years ago by vbraun

• Branch changed from u/chapoton/17251 to 8ce76ba086323151cbbd4227d51340749cb7ff2f
• Resolution set to fixed
• Status changed from positive_review to closed
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