#10963: More functorial constructions
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Reporter: nthiery | Owner: stumpc5
Type: enhancement | Status: needs_review
Priority: major | Milestone: sage-6.1
Component: categories | Resolution:
Keywords: days54 | Merged in:
Authors: Nicolas M. Thiéry | Reviewers: Simon King, Frédéric
Report Upstream: N/A | Chapoton
Branch: | Work issues:
public/ticket/10963 | Commit:
Dependencies: #11224, #8327, | dbb17b11bb9e8f94b5d9d3424cd34c5efc82564c
#10193, #12895, #14516, #14722, | Stopgaps:
#13589, #14471, #15069, #15094, |
#11688, #13394, #15150, #15506 |
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Comment (by nthiery):
Replying to [comment:331 nbruin]:
> Replying to [comment:330 nthiery]:
> Right. I was expecting something like that. The fact that each has to
refer to the other is suspicious to me. What is the scenario that makes
this absolutely necessary to be there right from the start? Wouldn't it be
possible for there to be only one link? Perhaps when that link is actually
exercised the other one can be put in place.
>
> My default reaction would be that !FiniteDimensionalAlgebras needs to
know about Algebras because it needs to inherit the properties of
Algebras, but is it absolutely necessary for Algebras to know about a
!FiniteDimensional version, even before it is instantiated? In general I
expect the !LazyImport to be a bad sign. !LazyImports have trouble getting
resolved in the first place. In fact, in the traceback that Volker
produced, you can see there are is a !LazyImport involved in the deep
recursion, so I suspect that the !LazyImport in this case indeed does not
get cleared properly.
>
> My default would be that `FiniteDimensionalAlgebras` only registers
itself with `Algebras` when it gets instantiated, if that is necessary at
all. That requires finding a solution for `Algebras().FiniteDimensional()`
(is that how you call it?) when that happens before
`FiniteDimensionalAlgebras` gets imported. Does that happen at all? If so,
what's the scenario? Perhaps we can solve that scenario.
As pointed by Simon, {{{Algebras().FiniteDimensional()}}} is usually
the default scenario. And it was an important design goal for me that
importing Algebras did not trigger the import of all its axiom
subcategories, because there can be many. For example, with my
upcoming patch on semigroups, I would not want that importing
semigroups (which is done at startup time) would trigger the import of
the categories of respectively LTrivial, RTrivial, JTrivial, DTrivial,
HTrivial, and Band semigroups, and their finite variants, since those
are only relevant to a small public.
The reverse scenario (where FiniteDimensionalAlgebras is called first)
is not as important but still is a nice and natural feature. One would
not usually think of using {{{DivisionRings().Commutative()}}} for
{{{Fields()}}} :-)
We could think of FiniteDimensionalAlgebras triggering the import of
Algebra, with some magic to put in place the link in
FiniteDimensionalAlgebras from that in Algebra. But it sounds to me
that this logic would be somewhat more complicated (searching through
the code to get the link) and not necessarily more robust than the
current name mangling.
Cheers,
Nicolas
--
Ticket URL: <http://trac.sagemath.org/ticket/10963#comment:337>
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