sparse linear algebra: nonzero_positions is slow

[boothby]

Currently, generic sparse matrices inherit their nonzero_positions method from matrix0.py. This should be trivial to fix.

def nonzero_positions(self):
    return self._entries.keys()

Component: linear algebra

Keywords: sparse

Issue created by migration from https://trac.sagemath.org/ticket/4648

[rlmill]

Attachment: trac-4648.patch.gz

[rlmill]

comment:2

Not quite so trivial as two lines, but...

[craigcitro]

comment:3

Code looks good. Merge!

However, I think that the fact that all three versions of this code are nearly identical means that a new enhancement ticket should be opened to clean up the classes here. In particular, I think the following might be a reasonable plan:

• in matrix_integer_sparse, rename _matrix to _rows for consistency (and clarity -- you're getting a list of rows, not a pointer to the whole matrix)
• clean up the associated vector classes (in fact, vector_modn_sparse isn't even a class right now!), and have them all inherit from an abstract class with the same methods they all share (which could all raise NotImplementedErrors, for all that matters)
• make each of the sparse matrix classes have a member _rows of type vector_sparse_generic or whatever, and then move the _nonzero_positions_by_row down to the generic class.

It would get rid of this code duplication, clean things up, etc.

[sagetrac-mabshoff]

comment:4

Merged in Sage 3.3.alpha2.

Cheers,

Michael