#18384: random_matrix with algorithm "subspaces" doesn't choose the rank
correctly
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Reporter: ddrake | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-6.7
Component: linear algebra | Resolution:
Keywords: matrix random rank | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Description changed by ddrake:
Old description:
> Using Sage 6.5, when I do
> {{{
> random_matrix(QQ, 7,4, algorithm='subspaces')
> }}}
> almost always it says
> {{{
> Error in lines 1-1
> Traceback (most recent call last):
> File "/projects/e51fbbc4-453b-
> 4f00a470028a1136adeb/.sagemathcloud/sage_server.py", line 879, in execute
> exec compile(block+'\n', '', 'single') in namespace, locals
> File "", line 1, in <module>
> File "/usr/local/sage/sage-6.5/local/lib/python2.7/site-
> packages/sage/matrix/constructor.py", line 1364, in random_matrix
> return random_subspaces_matrix(parent, *args, **kwds)
> File "/usr/local/sage/sage-6.5/local/lib/python2.7/site-
> packages/sage/matrix/constructor.py", line 3583, in
> random_subspaces_matrix
> raise ValueError("rank cannot exceed the number of rows or columns.")
> ValueError: rank cannot exceed the number of rows or columns.
> }}}
> If I run that many times, it does produce a matrix -- perhaps 5-10% of
> the time.
>
> The documentation says it randomly generates the rank, but it does not
> seem smart enough to generate a rank that is possible for the given
> dimensions.
New description:
Using Sage 6.5, when I do
{{{
random_matrix(QQ, 7,4, algorithm='subspaces')
}}}
almost always it says
{{{
Error in lines 1-1
Traceback (most recent call last):
File "/projects/e51fbbc4-453b-
4f00a470028a1136adeb/.sagemathcloud/sage_server.py", line 879, in execute
exec compile(block+'\n', '', 'single') in namespace, locals
File "", line 1, in <module>
File "/usr/local/sage/sage-6.5/local/lib/python2.7/site-
packages/sage/matrix/constructor.py", line 1364, in random_matrix
return random_subspaces_matrix(parent, *args, **kwds)
File "/usr/local/sage/sage-6.5/local/lib/python2.7/site-
packages/sage/matrix/constructor.py", line 3583, in
random_subspaces_matrix
raise ValueError("rank cannot exceed the number of rows or columns.")
ValueError: rank cannot exceed the number of rows or columns.
}}}
If I run that many times, it does produce a matrix -- perhaps 5-10% of the
time.
The documentation says it randomly generates the rank, but it does not
seem smart enough to generate a rank that is possible for the given
dimensions.
(If I specify the rank, the function does work as expected. But the
documentation seems to indicate that you can omit that and it will choose
a rank for you.)
--
--
Ticket URL: <http://trac.sagemath.org/ticket/18384#comment:1>
Sage <http://www.sagemath.org>
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