#18447: Implement dual-quasi-Schur basis in NCSF
-------------------------------------+-------------------------------------
       Reporter:  zabrocki           |        Owner:
           Type:  enhancement        |       Status:  new
       Priority:  minor              |    Milestone:  sage-6.7
      Component:  combinatorics      |   Resolution:
       Keywords:  ncsf, qsym,        |    Merged in:
  quasiSchur                         |    Reviewers:
        Authors:                     |  Work issues:
Report Upstream:  N/A                |       Commit:
         Branch:                     |  67263efe75616ab45a6a97e0205462c05612e5c2
  public/combinat/zabrocki/ncsf_quasi_schur_basis/18447|     Stopgaps:
   Dependencies:  #18415             |
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Comment (by zabrocki):

 I have restored the coercions `_on_basis` (rather than
 `_by_triangularity`) using transition matrices.  The main difference in
 the `QS` basis is that the coercion is to/from the monomial basis instead
 of the fundamental basis and the `_from_monomial_transition_matrix` calls
 `number_of_SSRCT`.  This is significantly faster than creating the
 `_from_fundmental_transition_matrix` using `CompositionTableaux`.

 Comparing to branch ​b8cefb8 (with a @cached_method in from of
 `_to_monomial_on_basis`)
 {{{
 sage: timeit('QS[1,2,1]*QS[2,2]',number=1,repeat=1)
 1 loops, best of 1: 46.3 s per loop
 sage: timeit('QS[1,2,1]*QS[2,3]',number=1,repeat=1)
 1 loops, best of 1: 421 s per loop
 }}}

 Same calculation on current branch
 {{{
 sage: timeit('QS[1,2,1]*QS[2,2]',number=1,repeat=1)
 1 loops, best of 1: 18.7 s per loop
 sage: timeit('QS[1,2,1]*QS[2,3]',number=1,repeat=1)
 1 loops, best of 1: 90.7 s per loop
 }}}

 I've optimized here the single calculation, but subsequent calculations
 are all cached and will be faster (and faster than my
 `_to/from_*_by_triangularity` methods).

--
Ticket URL: <http://trac.sagemath.org/ticket/18447#comment:17>
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