#9326: Add cohomology of toric varieties
----------------------------------+-----------------------------------------
   Reporter:  vbraun              |       Owner:  AlexGhitza  
       Type:  enhancement         |      Status:  needs_review
   Priority:  major               |   Milestone:  sage-4.5    
  Component:  algebraic geometry  |    Keywords:              
     Author:  Volker Braun        |    Upstream:  N/A         
   Reviewer:  Andrey Novoseltsev  |      Merged:              
Work_issues:                      |  
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Changes (by vbraun):

  * status:  needs_info => needs_review


Old description:

> This patch adds a cohomology ring to toric varieties. This is then used
> for characteristic classes.
>
> I'm using the usual description of the rational cohomology ring via the
> Stanley-Reisner ideal of the fan. This does not work for singular
> varities with worse than orbifold singularities. I don't have any good
> candidate for the "space where the Chern classes live" in that case.
>
> Prerequisites:
>   * #9245: Add library of toric varieties.
>   * #9429: Undesirable behaviour when deriving from `QuotientRingElement`

New description:

 This patch adds a cohomology ring to toric varieties. This is then used
 for characteristic classes.

 I'm using the usual description of the rational cohomology ring via the
 Stanley-Reisner ideal of the fan. This does not work for singular varities
 with worse than orbifold singularities. I don't have any good candidate
 for the "space where the Chern classes live" in that case.

 Prerequisites:
   * #9245: Add library of toric varieties.

--

Comment:

 Updated patch that implements classes `CohomologyRing` and
 `CohomologyClass`. These do not follow the coercion model since their
 superclasses `QuotientRing_generic` and `QuotientRingElement` have not
 been converted to the new coercion model. The new classes will easily
 convert to the new coercion model once `QuotientRing` and its subclasses
 are updated.

 First apply `trac_9326_QuotientRing_fix_derived_classes.patch` (which is
 just a renamed version of Andrey's
 `trac_9429_fix_derived_classes.2.patch`), then
 `trac_9326_toric_variety_cohomology.patch` on top.

-- 
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/9326#comment:11>
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