#13991: Mitigate speed regressions in symmetric function related code due to
#12313
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Reporter: nbruin | Owner: sage-combinat
Type: enhancement | Status: new
Priority: major | Milestone: sage-5.7
Component: combinatorics | Resolution:
Keywords: | Work issues:
Report Upstream: N/A | Reviewers:
Authors: | Merged in:
Dependencies: | Stopgaps:
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Comment (by nbruin):
Replying to [comment:6 SimonKing]:
> I expected that it would be called once, and then cached. But why is no
homset created, even though coercion maps should certainly be involved?
Probably the homsets are associated with the coercion maps.
Without #12313 coercion maps are blessed with eternal life (or at least as
long as the life of the object they are mapping ''to''), thus saving the
domains as well. When those domains are re-used, it finds the coercion map
that was stored and it doesn't need to create a new homset.
Note that `k_dual` gives a ''dual'' basis, so these are finitely generated
''quotients'' rather than finitely generated subspaces. I can imagine how
for a computer algebra system that means you end up with a more
complicated construction; one where you can more easily lose track of a
parent. If you end up recreating that think, you have to rediscover (and
construct!) the coercion; with its homset. In particular, to do
arithmetic, you always end up lifting and projecting down again. Something
that probably shouldn't be done via the coercion framework, since you
already know which homomorphism to apply, but clearly is done.
Also note that `k_dual` is one of the recent recent additions there and
has a different author list than the other files. It says explicitly that
it's ''based'' on similar code elsewhere. The authors might not have
carried through all the original design decision (and forgotten the
caching of some associated stucture somewhere)
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13991#comment:7>
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