#5184: [with patch, needs work] nonzero_positions is broken for sparse vectors
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Reporter: jhpalmieri | Owner: jhpalmieri
Type: defect | Status: assigned
Priority: major | Milestone: sage-3.4.1
Component: linear algebra | Keywords:
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Comment(by cwitty):
Instead of tests like {{{if a != 0:}}}, it should use {{{if a:}}}. The
code is a little uglier and harder to understand, but it's much faster;
these are approximations of the sorts of timing differences you would see:
{{{
sage: foo = QQbar(3)
sage: timeit('bool(foo)')
625 loops, best of 3: 1.24 µs per loop
sage: timeit('foo != 0r')
625 loops, best of 3: 100 µs per loop
sage: foo = 3
sage: timeit('bool(foo)')
625 loops, best of 3: 286 ns per loop
sage: timeit('foo != 0r')
625 loops, best of 3: 4.2 µs per loop
}}}
(Also, in the places where you deleted "A dense a sparse", is it worth
adding a note that says something like "(This is true even if one is
sparse and the other is dense.)"?)
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/5184#comment:4>
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