Bugfix concerning ticket #26421

[soehms]

In #26421 factorization of polynomials has been extended to previously untreated cases in which the polynomial's base ring is an integral domain. The factorization is done over the field of fraction and excepted if it can be coerced into the base ring itself. Since the method base_change of the class Factorzation doesn't check if the unit of the factorization is coerced to a unit again, this implementation is too vastly:

sage: R.<t> = LaurentPolynomialRing(ZZ)
sage: P.<x> = R[]
sage: f = 2*x + 4
sage: f.is_irreducible()
True
sage: F = f.factor(); F
(2) * (x + 2)
sage: F.unit()
2

[soehms]

Maybe a better place for the fix would be the method base_change of the class Factorization. But since this leads to the failure of previous doctests (in cases is_unit is not implemented), I preferred the implementation in method factor.

---

New commits:

​004c1c4

29266 initial version

[tscrim]

One little change: "coerce" to "convert". If it was a coercion map, then the fact it was a unit must be preserved (as coercions must be morphisms). Once you change that, you can set a positive review.

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​a21db27

29266: correction according to review

[soehms]

Thanks!