#12914: Representation theory of finite semigroups
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   Reporter:  nthiery        |             Owner:  tbd     
       Type:  PLEASE CHANGE  |            Status:  new     
   Priority:  major          |         Milestone:  sage-5.1
  Component:  PLEASE CHANGE  |          Keywords:          
Work issues:                 |   Report Upstream:  N/A     
  Reviewers:                 |           Authors:          
  Merged in:                 |      Dependencies:          
   Stopgaps:                 |  
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 Add support for representation theory of finite semigroups. Quite some
 stuff is available in the sage-combinat queue.

 * Required discussions about the current features:
  * What to merge now ; what to merge later
  * How to specify an indexing of the J-classes
  * Should JTrivial / ... be adjectives?
  * Should representation theory questions be asked to the semigroup or its
 algebra?
    * S.character_ring(QQ, ZZ) or S.algebra(QQ).character_ring(ZZ) ?
    * S.simple_modules(QQ) or S.algebra(QQ).simple_modules()?
  * Character rings
   * Should this be called Character ring?
   * How to specify the two base rings (for the representations / for the
 character ring)?
   * Should left and right characters live in the same space (with
 realizations)?
     e.g.:
     * Should there be coercions or conversions between the basis of left-
 class modules and right-class modules?
     * Should the basis of simple modules on the left and on the right be
 identified?
   * How to handle subspaces (like for projective modules when the Cartan
 matrix is not invertible)
  * If we discover that a semigroup is J-trivial, how to propagate this
 information to its algebra, character ring, ...?

 * Features that remain to be implemented:
  * is_r_trivial + _test_r_trivial and friends
  * Group of a regular J-class
  * Character table for any monoid
  * Cartan matrix for any monoid
  * Group of a non regular J-class
  * Cartan matrix by J-classes
  * Radical filtration of a module
  * Recursive construction of a triangular basis of the radical

-- 
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12914>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica, 
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