#12292: charpoly is recomputed when called with a different variable
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Reporter: zimmerma | Owner: jason, was
Type: enhancement | Status: new
Priority: minor | Milestone: sage-5.0
Component: linear algebra | Keywords: sd35.5
Work_issues: | Upstream: N/A
Reviewer: | Author:
Merged: | Dependencies:
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When the characteristic polynomial of a given matrix is computed for
two different variables, the computation is done once again:
{{{
sage: A=random_matrix(ZZ,100)
sage: time p1=A.charpoly('x')
Time: CPU 0.25 s, Wall: 0.28 s
sage: time p2=A.charpoly('x')
Time: CPU 0.00 s, Wall: 0.00 s
sage: time p3=A.charpoly('y')
Time: CPU 0.25 s, Wall: 0.29 s
sage: p1.subs(x=y) - p3
0
}}}
We see that the computation of p2 is immediate since it was cached
for the variable x, but that of p3 is not, since the code searches for a
cached charpoly with the variable y! It would suffice to search a cached
charpoly for any variable, and substitute that variable.
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12292>
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