#9455: Dimensions of eigenspaces for the Atkin-Lehner operator acting on modular
forms
-------------------------+-------------------------------------------------
       Reporter:  ljpk   |        Owner:  craigcitro
           Type:         |       Status:  needs_work
  enhancement            |    Milestone:  sage-6.9
       Priority:  minor  |   Resolution:
      Component:         |    Merged in:
  modular forms          |    Reviewers:
       Keywords:  atkin  |  Work issues:
  lehner                 |       Commit:
        Authors:  Lloyd  |  311782f16080ea75c9cef9671d92b50a6f570785
  Kilford                |     Stopgaps:
Report Upstream:  N/A    |
         Branch:         |
  u/chapoton/9455        |
   Dependencies:         |
-------------------------+-------------------------------------------------
Changes (by davidloeffler):

 * status:  needs_review => needs_work


Comment:

 This needs some serious work.

 - Most of this new code is added via methods of Gamma0 modular forms space
 objects. However, these objects can have any weight, but the
 implementations here only work for weight 2, so you can type something
 like
 {{{
  sage: ModularForms(1000003, 4).atkin_lehner_eigenspace_dimensions()
 }}}
  and it will silently return wrong output. More importantly, lots of these
 methods (e.g. {{{atkin_lehner_ramification}}}) are computing geometric
 properties of the underlying modular curves, so they belong in
 {{{sage.modular.arithgroup.congroup_gamma0}}}. Similarly,
 "primitive_ideal_number" should probably be a method of order objects, not
 a standalone function.

 - Many function names are mysterious or downright misleading, e.g. the
 method {{{modular_genus_X0}}} is not actually computing the genus of
 anything in most cases.

 - The documentation is poor. What on earth is the "(M, R)-old subspace"?
 What are "cyclic ideals"?  Docstrings for each method should explain what
 the arguments mean. The docstring for {{{old_subspace_dimension(self, M,
 R, w)}}} does not even mention Atkin--Lehner involutions!

 - Why is a line of code in the number fields module (in
 {{{absolute_order_from_module_generators}}}) deleted without explanation?

--
Ticket URL: <http://trac.sagemath.org/ticket/9455#comment:25>
Sage <http://www.sagemath.org>
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