#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 SimonKing):
I don't think that `Partitions(n)` has ever been cached. `Partitions` is a
function which apparently does not use a cache, and the object returned by
`Partitions(1)` is not an instance of `UniqueRepresentation`.
Actually, Partitions(1) is not a unique parent - and I think this actually
is the problem. Namely, we have
{{{
sage: P = Partitions(1)
sage: P is Partitions(1)
False
sage: P == Partitions(1)
True
}}}
In the old way of caching homsets, domain and codomain were tested for
equality. But now, they are tested for ''identity''. Hence, we now have
{{{
sage: H = Hom(Partitions(0),SymmetricFunctionAlgebra(QQ))
sage: H is Hom(Partitions(0),SymmetricFunctionAlgebra(QQ))
False
}}}
which used to return True, because Hom was caching by equality.
Hence, rather than having less caching, I actually suggest to have
''more'' caching in this case: `Partitions_n` should inherit from
`UniqueRepresentation`, or, if this is impossible, `Partitions` should be
equipped with a cache.
This cache should either be a weak cache, or it should be semi-weak (e.g.,
cache the output of `Partitions(n)` permanently for `n<256`, but weakly
for greater values).
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13991#comment:13>
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