#5976: [with patch; needs work] Add an Elliptic Curve Isogeny object
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 Reporter:  shumow         |       Owner:  shumow         
     Type:  enhancement    |      Status:  assigned       
 Priority:  major          |   Milestone:  sage-4.0.1     
Component:  number theory  |    Keywords:  Elliptic Curves
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Comment(by cremona):

 That all sounds very good to me.  Yes, over the rationals (and number
 fields) one is definitely interested in having specific models of the
 codomain.  We can add extra bits for the number field case later.

 There are of course some striking differences between the number field and
 finite field cases.  Over finite fields, when two curves are isogenous
 there are infinitely many isogenies (e.g.in the ordinary case, the
 isogenies form a rank 1 projective module over the endommorphism ring), so
 it would not be sufficient just to give the two curves;  one might also
 want to give a possible degree.  While over number fields (amd more
 generally in char. 0) there is less choice.

 John

-- 
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/5976#comment:20>
Sage <http://sagemath.org/>
Sage - Open Source Mathematical Software: Building the Car Instead of 
Reinventing the Wheel

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