#11875: Correct general brokenness of Farey symbols
-----------------------------+----------------------------------------------
Reporter: davidloeffler | Owner: craigcitro
Type: defect | Status: new
Priority: blocker | Milestone: sage-4.7.2
Component: modular forms | Keywords: modular subgroup
Work_issues: | Upstream: N/A
Reviewer: | Author:
Merged: | Dependencies:
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Description changed by leif:
Old description:
> The new Farey symbols code from #11709 needs some serious work before it
> can be allowed into a production release of Sage.
>
> See [http://groups.google.com/group/sage-
> devel/browse_thread/thread/e6b65915cde174b this sage-devel thread].
>
> As an absolute minimum, we should:
>
> * remove the file "sage.modular.arithgroup.noncongruence_example" (which
> is makes outrageously false mathematical statements in its docstrings --
> the "example noncongruence subgroup" is actually the congruence subgroup
> {{{GammaH(8, [5])}}} -- and is implemented in a stupidly broken way with
> no doctests and no usable methods whatsoever)
>
> * bring doctest coverage for the Python and Cython files in
> sage/modular/arithgroup back up to 100%, and make sure there are
> loads/dumps tests for all the classes;
>
> * make sure that the Farey symbol code works with all of the subclasses
> of ArithmeticSubgroup and add doctests to prove it;
>
> * add a warning in the documentation that commands like "index" and
> "generators" in Farey symbol code return the index, generators etc of the
> image of the group in PSL2Z, whereas Sage's general design is to work
> with subgroups of SL2Z.
New description:
The new Farey symbols code from #11709 needs some serious work before it
can be allowed into a production release of Sage.
See [http://groups.google.com/group/sage-
devel/browse_thread/thread/e6b65915cde174b this sage-devel thread].
As an absolute minimum, we should:
* Remove the file `sage.modular.arithgroup.noncongruence_example` (which
makes outrageously false mathematical statements in its docstrings -- the
"example noncongruence subgroup" is actually the congruence subgroup
{{{GammaH(8, [5])}}} -- and is implemented in a stupidly broken way with
no doctests and no usable methods whatsoever).
* Bring doctest coverage for the Python and Cython files in
`sage/modular/arithgroup/` back up to 100%, and make sure there are
`loads()`/`dumps()` tests for all the classes.
* Make sure that the Farey symbol code works with all of the subclasses
of `ArithmeticSubgroup` and add doctests to prove it.
* Add a warning in the documentation that commands like "index" and
"generators" in Farey symbol code return the index, generators etc. of the
image of the group in PSL2Z, whereas Sage's general design is to work with
subgroups of SL2Z.
--
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/11875#comment:1>
Sage <http://www.sagemath.org>
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