#12292: charpoly is recomputed when called with a different variable
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Reporter: zimmerma | Owner: jason, was
Type: enhancement | Status: needs_review
Priority: minor | Milestone: sage-5.0
Component: linear algebra | Keywords: sd35.5
Work_issues: | Upstream: N/A
Reviewer: Paul Zimmermann | Author: Michael Orlitzky
Merged: | Dependencies:
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Comment(by rbeezer):
A few comments from Review Days:
1. For a matrix A, you can examine A._cache directly. Instead of doing
timings, might it be better to check the cached value before and after the
second request (the one with a new variable specified)? A return value
with the new variable and a cached value with the original variable would
strike me as sufficient evidence, and superior to using timings in a
doctest.
1. In poking around with this it appears that the algorithm name is
part of the cache key in some instances, while there are places (eg
determinant computations) that just check for the "charpoly" cache key.
1. Applies on 5.0-beta8, FWIW.
{{{
sage: A = random_matrix(QQ, 3)
sage: A.charpoly()
x^3 + x^2 + 3*x - 13
sage: A._cache
{'clear_denom': ([ 1 0 -2]
[-2 -1 -2]
[ 0 2 -1], 1), 'charpoly_linbox': x^3 + x^2 + 3*x - 13}
sage: A.charpoly('t')
t^3 + t^2 + 3*t - 13
sage: A._cache
{'clear_denom': ([ 1 0 -2]
[-2 -1 -2]
[ 0 2 -1], 1), 'charpoly_linbox': x^3 + x^2 + 3*x - 13}
sage: A._cache['charpoly_linbox']
x^3 + x^2 + 3*x - 13
}}}
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12292#comment:6>
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