Opened 4 months ago
Closed 4 months ago
#31178 closed defect (fixed)
inverse_image of element fails for morphism of quotient rings
Reported by: | rburing | Owned by: | |
---|---|---|---|
Priority: | major | Milestone: | sage-9.3 |
Component: | algebra | Keywords: | inverse_image, hom, quotient |
Cc: | gh-mwageringel | Merged in: | |
Authors: | Markus Wageringel | Reviewers: | Ricardo Buring |
Report Upstream: | N/A | Work issues: | |
Branch: | 1e5b979 (Commits, GitHub, GitLab) | Commit: | 1e5b9796e14b40003d870384d8115e58857099a5 |
Dependencies: | Stopgaps: |
Description
Reported in Ask SageMath question #55099:
sage: R.<x, y> = QQ[] sage: R1 = R.quotient(R.ideal(y^2 - x^3)) sage: R2 = R.quotient(R.ideal(x)) sage: h = R1.hom([R2(y^2), R2(y^3)], R2) sage: h(R1(x)) ybar^2 sage: h.inverse_image(R2(y^2)) ... ValueError: element ybar^2 does not have preimage
Change History (3)
comment:1 Changed 4 months ago by
- Branch set to u/gh-mwageringel/31178
- Commit set to 1e5b9796e14b40003d870384d8115e58857099a5
- Status changed from new to needs_review
comment:2 Changed 4 months ago by
- Reviewers set to Ricardo Buring
- Status changed from needs_review to positive_review
Thanks for the fast reply. The new check looks good.
comment:3 Changed 4 months ago by
- Branch changed from u/gh-mwageringel/31178 to 1e5b9796e14b40003d870384d8115e58857099a5
- Resolution set to fixed
- Status changed from positive_review to closed
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Thanks for reporting this. The problem was that quotient rings can have generators which are constant:
Because of this, the check for testing whether an element is contained in the subring generated by certain variables failed.
I have replaced the check by a better and clearer one, which should resolve the issue.
New commits:
31178: fix inverse image for quotient rings