improve _vector_times_matrix

[sagetrac-ylchapuy]

Very small patch avoiding multiple copies

Component: linear algebra

Author: Yann Laigle-Chapuy

Reviewer: William Stein

Merged: Sage 4.1.2.alpha4

Issue created by migration from https://trac.sagemath.org/ticket/6968

[sagetrac-ylchapuy]

Attachment: trac_6968_vector_times_matrix.patch.gz

[sagetrac-ylchapuy]

comment:1

for the record:

before:

sage: m=identity_matrix(1000,sparse=True)
sage: v=vector([1]*1000,sparse=True)
sage: time p = v*m
CPU times: user 2.26 s, sys: 0.00 s, total: 2.26 s
Wall time: 2.26 s 

after:

sage: m=identity_matrix(1000,sparse=True)
sage: v=vector([1]*1000,sparse=True) 
sage: time p = v*m 
CPU times: user 0.20 s, sys: 0.00 s, total: 0.20 s
Wall time: 0.21 s

[williamstein]

comment:4

Nice!!

[sagetrac-mvngu]

Merged: Sage 4.1.2.alpha3

[sagetrac-mvngu]

Reviewer: William Stein

[sagetrac-mvngu]

comment:6

There is no 4.1.2.alpha3. Sage 4.1.2.alpha3 was William Stein's release for working on making the notebook a standalone package.

[sagetrac-mvngu]

Changed merged from Sage 4.1.2.alpha3 to Sage 4.1.2.alpha4