#15303: Coercion discovery fails to be transitive
-------------------------------------+-------------------------------------
Reporter: nbruin | Owner:
Type: defect | Status: needs_review
Priority: major | Milestone: sage-5.13
Component: coercion | Resolution:
Keywords: | Merged in:
Authors: Simon King | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
u/SimonKing/ticket/15303 | f837cbee8f81c4946a92193c73e86449c53515d9
Dependencies: #14711 | Stopgaps:
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Changes (by {'newvalue': u'Simon King', 'oldvalue': ''}):
* status: new => needs_review
* author: => Simon King
Comment:
I have pushed a new commit that implements version numbers for the
coercion cache, and I added a doctest along the following lines:
{{{
sage: class pA(Parent): pass
sage: class pB(Parent): pass
sage: class pC(Parent): pass
sage: A=pA(); B=pB(); C=pC()
sage: BtoA=Hom(B,A)(lambda x: A(x))
sage: AtoC=Hom(A,C)(lambda x: C(x))
sage: A.register_coercion(BtoA)
sage: C.coerce_map_from(B)
sage: A.register_embedding(AtoC)
sage: C.coerce_map_from(B)
Composite map:
From: <class '__main__.pB'>
To: <class '__main__.pC'>
WARNING: This map has apparently been used internally
in the coercion system. It may become defunct in the next
garbage collection. Please use a copy.
}}}
Hence, I think that the current commit solves our problem. In spite of the
following "todo" list, I put it to "needs review" (but I am sure that
further commits will be pushed soon).
TODO:
- Add documentation, stating that registering of coercions should ''only''
be done during initialisation, and that registering of embeddings
shouldn't be done too often.
- Run all doctests---since playing with the coercion digraph is asking for
trouble, I wouldn't be surprised about bad surprises `:-P`
- '''Important:''' Get timings for examples that should be most sensitive
against slow-downs in coercion.
--
Ticket URL: <http://trac.sagemath.org/ticket/15303#comment:14>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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