#11598: Congruence testing for odd modular subgroups
---------------------------------+------------------------------------------
Reporter: davidloeffler | Owner: craigcitro
Type: defect | Status: positive_review
Priority: major | Milestone: sage-pending
Component: modular forms | Keywords: modular congruence subgroup
Work_issues: | Upstream: N/A
Reviewer: Vincent Delecroix | Author: David Loeffler
Merged: | Dependencies: #11422
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Old description:
> The new functionality added in ticket #11422 makes it possible to
> manipulate arbitrary finite index (not necessarily congruence) subgroups
> of SL2Z. This massively extends my old code which only worked for
> subgroups containing -1.
>
> The "is_congruence" method in the new code, though, *defines* a subgroup
> to be congruence if its image modulo -1 is a congruence subgroup of
> PSL2Z. This is not the same as the conventional definition of a
> congruence subgroup of SL2Z. The patch below modifies the algorithm so it
> uses the conventional notion of "congruence". It also adds functionality
> for enumerating all the liftings of a projective modular subgroup.
>
> Part of a series of tickets: #10335 - #11422 - this one - #5048 - #10453
> - #11601.
>
> '''Apply:'''
> 1. [attachment:trac_11598-all.patch]
> 1. [attachment:trac_11598-docfixes.patch]
New description:
The new functionality added in ticket #11422 makes it possible to
manipulate arbitrary finite index (not necessarily congruence) subgroups
of SL2Z. This massively extends my old code which only worked for
subgroups containing -1.
The "is_congruence" method in the new code, though, *defines* a subgroup
to be congruence if its image modulo -1 is a congruence subgroup of PSL2Z.
This is not the same as the conventional definition of a congruence
subgroup of SL2Z. The patch below modifies the algorithm so it uses the
conventional notion of "congruence". It also adds functionality for
enumerating all the liftings of a projective modular subgroup.
Part of a series of tickets: #10335 - #11422 - this one - #5048 - #10453 -
#11601.
'''Apply:'''
1. [attachment:trac_11598-foldedrebased.patch]
--
Comment(by davidloeffler):
The unpickling bug that I recently spotted and fixed at #11422 causes the
patches here to fail to merge. I've rebased the relevant patches and
qfolded them into a single patch. As there is no change to the actual
code, I hope it's fair to leave this as positive review.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/11598#comment:15>
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