Opened 13 years ago
Closed 4 years ago
#6392 closed defect (fixed)
modular abelian quotient -- something goes wrong
Reported by: | was | Owned by: | craigcitro |
---|---|---|---|
Priority: | major | Milestone: | sage-8.4 |
Component: | modular forms | Keywords: | |
Cc: | mderickx | Merged in: | |
Authors: | Kevin Lui | Reviewers: | Frédéric Chapoton |
Report Upstream: | N/A | Work issues: | |
Branch: | 0bc6f5a (Commits, GitHub, GitLab) | Commit: | 0bc6f5a1c37f5a93e00d1fb4ecd4feaae7b35839 |
Dependencies: | Stopgaps: | todo |
Description
This isn't right:
sage: J = J0(43) sage: G,_ = J[0].intersection(J[1]) sage: J[1]/G Simple abelian subvariety 43b(1,43) of dimension 2 of J0(43)
This is
sage: J[0]/G (Abelian variety factor of dimension 1 of J0(43), Abelian variety morphism: From: Simple abelian subvariety 43a(1,43) of dimension 1 of J0(43) To: Abelian variety factor of dimension 1 of J0(43))
For some reason J[1]/G isn't even creating the right output (i.e., pair (abvar, map)).
Change History (15)
comment:1 Changed 12 years ago by
- Cc mderickx added
- Report Upstream set to N/A
comment:2 Changed 12 years ago by
My confusion mainly comes from the following:
sage: J[1].finite_subgroup(G) Finite subgroup with invariants [] over QQ of Simple abelian subvariety 43b(1,43) of dimension 2 of J0(43) J[1].intersection(G) Finite subgroup with invariants [2, 2] over QQ of Simple abelian subvariety 43b(1,43) of dimension 2 of J0(43)
comment:3 Changed 9 years ago by
- Milestone changed from sage-5.11 to sage-5.12
comment:4 Changed 8 years ago by
- Milestone changed from sage-6.1 to sage-6.2
comment:5 Changed 8 years ago by
- Milestone changed from sage-6.2 to sage-6.3
comment:6 Changed 8 years ago by
- Milestone changed from sage-6.3 to sage-6.4
comment:7 Changed 7 years ago by
- Stopgaps set to todo
comment:8 Changed 4 years ago by
- Branch set to u/klui/finite_subgroup
comment:9 Changed 4 years ago by
- Commit set to 0bc6f5a1c37f5a93e00d1fb4ecd4feaae7b35839
The issue was in finite_subgroup
. We had to include the lattice of the ambient jacobian and not just the ambient abelian subvariety.
This branch returns the identity map as well when quotienting by a trivial group.
New commits:
0bc6f5a | quotient by trivial subgroup now returns identity map, finite_subgroup now works when subgroup has different ambient variety
|
comment:10 Changed 4 years ago by
- Status changed from new to needs_review
comment:11 Changed 4 years ago by
- Reviewers set to Frédéric Chapoton
- Status changed from needs_review to positive_review
ok, let it be. Please add author full name.
comment:12 Changed 4 years ago by
- Milestone changed from sage-6.4 to sage-8.4
comment:13 Changed 4 years ago by
- Status changed from positive_review to needs_work
Author name is missing..
comment:14 Changed 4 years ago by
- Status changed from needs_work to positive_review
comment:15 Changed 4 years ago by
- Branch changed from u/klui/finite_subgroup to 0bc6f5a1c37f5a93e00d1fb4ecd4feaae7b35839
- Resolution set to fixed
- Status changed from positive_review to closed
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G is strictly speaking not a subgroup of J[1] in this example it's a subgroup of J[0]. What happens if you travel down the code is equivalent to this:
Now the source code of _quotient_by_finite_subgroup is
So i guess it should instead return
There is also a problem with the is_subgroup code: sage: G.is_subgroup(J[1]) True This error is caused by the intersection code: sage: G.intersection(J[1]) Finite subgroup with invariants [2, 2] over QQ of Simple abelian subvariety 43b(1,43) of dimension 2 of J0(43)
Maybe I'm a bit confused but is the intersection of abelian varieties defined in an other way than just the set theoretic one. Because by reading the source code I really get the feeling that it does. The errors certainly seem to come from different assumtions about this in different parts of the code.