#4483: Add coefficient_field() method to ModularSymbols/ModularForms
-----------------------------+----------------------------------------------
   Reporter:  jonhanke       |       Owner:  craigcitro
       Type:  enhancement    |      Status:  new       
   Priority:  minor          |   Milestone:  sage-4.3.1
  Component:  modular forms  |    Keywords:            
Work_issues:                 |      Author:            
   Upstream:  N/A            |    Reviewer:            
     Merged:                 |  
-----------------------------+----------------------------------------------
Changes (by AlexGhitza):

  * upstream:  => N/A


Old description:

> ## Define a newform (up to conjugation)
> `time nf =
> ModularSymbols(100,2,1).cuspidal_subspace().new_subspace().decomposition()[0]`
>
> `nf.coefficient_field()` -- should return the field of definition of the
> newform.  (This appears to be accomplished with
> `nf.eigenvalue(1).parent()`.  It would be nice to know that this really
> does give the field of definition.)
>
> `nf.degree()` -- should return the degree of the coefficient field.

New description:

 Define a newform (up to conjugation)

 {{{
 time nf =
 ModularSymbols(100,2,1).cuspidal_subspace().new_subspace().decomposition()[0]
 }}}

 `nf.coefficient_field()` -- should return the field of definition of the
 newform.  (This appears to be accomplished with
 `nf.eigenvalue(1).parent()`.  It would be nice to know that this really
 does give the field of definition.)

 `nf.degree()` -- should return the degree of the coefficient field.

--

Comment:

 There is something like this in Sage: look at the class {{{Newform}}} in
 modular/modform/element.py.  It has a method
 {{{hecke_eigenvalue_field()}}} which returns the field of definition of
 the newform.  There is no {{{degree()}}} method, although that's of course
 easy to get at this point as {{{nf.hecke_eigenvalue_field().degree()}}}.

 It remains to add such a method to modular symbols
 ({{{nf.eigenvalue(1).parent()}}} is indeed correct), and maybe make
 {{{coefficient_field()}}} an alias for {{{hecke_eigenvalue_field()}}}.

-- 
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/4483#comment:1>
Sage <http://www.sagemath.org>
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