#18312: Construction of a sparse matrix from sparse vectors does not exploit
sparseness
------------------------------+----------------------------
Reporter: nthiery | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-6.7
Component: linear algebra | Keywords:
Merged in: | Authors:
Reviewers: | Report Upstream: N/A
Work issues: | Branch:
Commit: | Dependencies:
Stopgaps: |
------------------------------+----------------------------
{{{
sage: n = 10^3
sage: F = FreeModule(QQ, n, sparse=True)
sage: v = F.an_element()
sage: vectors = [v]*n
sage: %time a = matrix(vectors, sparse=True)
CPU times: user 2.01 s, sys: 38.4 ms, total: 2.05 s
Wall time: 1.96 s
}}}
Compare with the construction of the same matrix through an
intermediate dictionary:
{{{
sage: %time b = matrix(QQ, n, {(i,j): c for i,v in enumerate(vectors) for
j,c in v.iteritems()}, sparse=True)
CPU times: user 7.33 ms, sys: 124 µs, total: 7.46 ms
Wall time: 6.06 ms
sage: a == b
True
}}}
Running `%prun` shows that the input vectors are converted to dense
lists and back (gasp), which gives a complexity of `n^2` instead of
linear in the number of nonzero entries as would be expected.
--
Ticket URL: <http://trac.sagemath.org/ticket/18312>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
--
You received this message because you are subscribed to the Google Groups
"sage-trac" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send email to [email protected].
Visit this group at http://groups.google.com/group/sage-trac.
For more options, visit https://groups.google.com/d/optout.
