#14711: Weak references in the coercion graph
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Reporter: jpflori | Owner: davidloeffler
Type: defect | Status: needs_review
Priority: critical | Milestone: sage-5.13
Component: number fields | Resolution:
Keywords: memleak, number | Merged in:
field, QuadraticField | Reviewers:
Authors: Simon King | Work issues:
Report Upstream: N/A | Commit:
Branch: | 364b9856b28d7060e3ea9825144de66c8f11ca2a
u/SimonKing/ticket/14711 | Stopgaps:
Dependencies: |
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Comment (by nbruin):
Replying to [comment:132 SimonKing]:
> Why? What should be done with these embeddings?
I don't have a direct application in mind (hence the ''might''), but just
for symmetry it seems appropriate.
One possible example would be someone working on some weak approximation
problem, having a whole bunch of number fields K with specified embeddings
in CC as well as Qp (for some p). In this application, Qp may well be just
as immortal as CC is, so using register_coercion would not express the
right life time implications: The K should get deleted while Qp remains,
just as CC remains.
This would be accomplished by letting K have embeddings in both CC and
Qp. I'm not claiming at this point that using coercion is the most
appropriate tool to express the relations in this scenario.
There is one benefit one gets from having maps recognized as coercions: A
lot of derived structures can now be automatically get built with the
appropriate maps between them via pushout constructions. If you just have
some maps lying around, constructing the corresponding derived maps will
be a lot of work.
That's my reason to really care about an expressive coercion system. My
experience with magma, which tends to have a much more restricted notion
of coercion, has taught me that building these maps can be a *lot* of
silly work. It would be great if one could "borrow" the coercion system
for that every now and again (this is one of the reasons why I think some
context manager that can put in "temporary" coercions would be great:
inside the context manager one would request the derived map, store it,
and then return the coercion system to its original state)
--
Ticket URL: <http://trac.sagemath.org/ticket/14711#comment:133>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
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