#11544: Viewing matrices of algebraic numbers can take a long time
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Reporter: rbeezer | Owner: jason, was
Type: defect | Status: needs_review
Priority: major | Milestone: sage-4.7.2
Component: linear algebra | Keywords:
Work_issues: | Upstream: N/A
Reviewer: | Author:
Merged: | Dependencies:
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Changes (by rbeezer):
* status: new => needs_review
Old description:
> The following code leads to about a one minute hang for me (reproducibly
> in a fresh session). Keshav Kini (via IRC) had the same experience.
>
> {{{
> sage: A = matrix(QQ, 4, 4, [1, 2, -2, 2, 1, 0, -1, -1, 0, -1, 1, 1, -1,
> 2, 1/2, 0])
> sage: e = A.eigenvalues()[3]
> sage: K = (A-e).kernel()
> sage: P = K.basis_matrix()
> sage: x = P.list()[3]
> sage: remap = {}
> sage: remap.has_key(x)
> }}}
>
> This behavior hangs the creation of a string version of a matrix. If you
> comment-out {{{sage/matrix/matrix0.pyx}}} at lines 1695-1696, the problem
> goes away. To see the effect, run the first four lines of the code above
> and then just print P, with and without the two lines mentioned.
>
> I have a workaround in mind that may solve the problem in many cases.
> Root issue is at #11543.
New description:
The following code leads to about a one minute hang for me (reproducibly
in a fresh session). Keshav Kini (via IRC) had the same experience.
{{{
sage: A = matrix(QQ, 4, 4, [1, 2, -2, 2, 1, 0, -1, -1, 0, -1, 1, 1, -1, 2,
1/2, 0])
sage: e = A.eigenvalues()[3]
sage: K = (A-e).kernel()
sage: P = K.basis_matrix()
sage: x = P.list()[3]
sage: remap = {}
sage: remap.has_key(x)
}}}
This behavior hangs the creation of a string version of a matrix. If you
comment-out {{{sage/matrix/matrix0.pyx}}} at lines 1695-1696, the problem
goes away. To see the effect, run the first four lines of the code above
and then just print P, with and without the two lines mentioned.
I have a workaround in mind that may solve the problem in many cases.
Root issue is at #11543.
'''Apply:'''
1. [attachment:trac_11544-avoid-hash-of-matrix-entries.patch]
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/11544#comment:2>
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