#12348: variable ind has the wrong type in matrix indexing; and why are big
sparse
matrices so slow to make?
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Reporter: was | Owner: jason, was
Type: defect | Status: new
Priority: minor | Milestone: sage-5.0
Component: linear algebra | Keywords:
Work_issues: | Upstream: N/A
Reviewer: | Author:
Merged: | Dependencies:
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Oops, in the function {{{def __getitem__(self, key)}}} in matrix0.pyx,
the variable {{{ind}}} is of type int.
This will work fine on 32-bit, but will be totally broken/buggy in subtle
and surprising ways on 64-bit machines. The type of ind should be
{{{Py_ssize_t}}}, just like the type of {{{i}}}. Nobody will notice this
now, because there is some sort of massive weird inefficiency in the
creation of sparse matrices (maybe the parent space has its basis
constructed or something idiotic like that), which makes it impossible to
make a large sparse matrix, even though this should be trivial, instant,
fast, and take no memory:
{{{
sage: time a = matrix(QQ, 2^25, sparse=True)
Time: CPU 5.88 s, Wall: 8.46 s
sage: get_memory_usage() # what ?
3908.29296875
}}}
The ind being an int was introduced in #4973.
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12348>
Sage <http://www.sagemath.org>
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