#12170: Genus computation (using singular) and _singular_ object for function 
filed
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   Reporter:  sydahmad            |          Owner:  AlexGhitza                 
    
       Type:  enhancement         |         Status:  needs_review               
    
   Priority:  minor               |      Milestone:  sage-5.0                   
    
  Component:  algebraic geometry  |       Keywords:  function field, genus, 
singular
Work_issues:                      |       Upstream:  N/A                        
    
   Reviewer:                      |         Author:  Syed Ahmad Lavasani        
    
     Merged:                      |   Dependencies:  9054                       
    
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Changes (by sydahmad):

  * status:  new => needs_review


Comment:

 if we have:

 kx.<x> = FunctionField(QQ)
 kxY.<Y> = PolynomialRing(QQ)

 kxY._singular_ should be k(x)[Y] (which is what this code generates)
 however, singular only computes the genus of an ideal of k[x][Y] ring. So,
 I have to generate a tmpR = k[x][Y] each time I need to compute the genus.
 Maybe it's worth it to add __singular_deg2_ private object to store this
 ring as well.

 Also, it makes sense to store the genus in __genus. But I'm not sure how
 should I check it's validity. Can the defining polynomial of the function
 field change after its creation. If not then we can set __genus = -1 and
 if it's non-negative then it's valid.

-- 
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12170#comment:1>
Sage <http://www.sagemath.org>
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