#715: Parents probably not reclaimed due to too much caching
----------------------------+-----------------------------------------------
Reporter: robertwb | Owner: somebody
Type: defect | Status: needs_work
Priority: major | Milestone: sage-4.8
Component: coercion | Keywords: weak cache coercion
Work_issues: fix doctests | Upstream: N/A
Reviewer: | Author: Simon King
Merged: | Dependencies: #9138, #11900
----------------------------+-----------------------------------------------
Comment(by SimonKing):
PS: Note that vector spaces with different inner product are considered
equal.
{{{
sage: V = QQ^5
sage: M = random_matrix(QQ,5,5)
sage: M.set_immutable()
sage: W = VectorSpace(QQ,5,inner_product_matrix=M)
sage: V
Vector space of dimension 5 over Rational Field
sage: W
Ambient quadratic space of dimension 5 over Rational Field
Inner product matrix:
[ 0 1/2 1 -1 -1]
[ 0 0 0 1 -1/2]
[ -2 0 0 0 0]
[ 1 0 2 0 0]
[ 0 -2 0 1 0]
sage: V==W
True
sage: type(V)==type(W)
False
}}}
But this is not the problem here: The two equal vector spaces involved in
the crash have default inner product.
The non-uniqueness makes me think of another potential solution: The
coercion model has a method "verify_action". This is ''only'' called when
a new action is found, but not when an action is taken from the cache.
So, in addition to fixing the non-unique vector space in the modular
symbols code, one could ''always'' verify the action. Probably this would
be too slow, though.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/715#comment:55>
Sage <http://www.sagemath.org>
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