Opened 4 years ago
Closed 3 years ago
#26817 closed defect (fixed)
GaloisGroup_subgroup.fixed_field() should always return an embedding
Reported by: | pbruin | Owned by: | |
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Priority: | minor | Milestone: | sage-9.0 |
Component: | number fields | Keywords: | Galois group |
Cc: | davidloeffler | Merged in: | |
Authors: | Peter Bruin | Reviewers: | David Roe |
Report Upstream: | N/A | Work issues: | |
Branch: | 2b26bc4 (Commits, GitHub, GitLab) | Commit: | 2b26bc454ddbf132ab5c41ef90b86d713735a1ad |
Dependencies: | Stopgaps: |
Description
Currently, GaloisGroup_subgroup.fixed_field()
does not return an embedding of the fixed field into the ambient field if the subgroup is trivial:
sage: K.<a> = NumberField(x^6 - 6*x^4 + 9*x^2 + 23) sage: G = K.galois_group() sage: H = G.subgroup([g for g in G if g.order().divides(3)]) sage: H.fixed_field() (Number Field in a0 with defining polynomial x^2 + 207, Ring morphism: From: Number Field in a0 with defining polynomial x^2 + 207 To: Number Field in a with defining polynomial x^6 - 6*x^4 + 9*x^2 + 23 Defn: a0 |--> 3*a^3 - 9*a) sage: H = G.subgroup([G.identity()]) sage: H.fixed_field() Number Field in a with defining polynomial x^6 - 6*x^4 + 9*x^2 + 23
This should be fixed for consistency.
Change History (5)
comment:1 Changed 4 years ago by
Branch: | → u/pbruin/26817-GaloisGroup_fixed_field |
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Cc: | davidloeffler added |
Commit: | → 9545ec7da42286552422f245a2d9b4f99393beeb |
Status: | new → needs_review |
comment:2 Changed 4 years ago by
Commit: | 9545ec7da42286552422f245a2d9b4f99393beeb → 2b26bc454ddbf132ab5c41ef90b86d713735a1ad |
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comment:3 Changed 3 years ago by
Reviewers: | → David Roe |
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Status: | needs_review → positive_review |
Looks good to me. The recent test failures are due to the switch to Python 3 breaking patchbots.
comment:4 Changed 3 years ago by
Milestone: | sage-8.5 → sage-9.0 |
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comment:5 Changed 3 years ago by
Branch: | u/pbruin/26817-GaloisGroup_fixed_field → 2b26bc454ddbf132ab5c41ef90b86d713735a1ad |
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Resolution: | → fixed |
Status: | positive_review → closed |
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This branch fixes the problem by removing two lines that "work around a silly error". David, you seem to be the author of this code; do you remember what this was? Maybe a bug in an old PARI version?