[SciPy-User] Can I copy a sparse matrix into an existing dense numpy matrix?

Conrad Lee conradlee@gmail....
Mon Feb 6 08:56:22 CST 2012

Warren, thanks for the suggestion with the COO matrix.  In general I'm
storing sparse matrices in the CSR format for quick multiplication, so your
approach would mean that I have to convert to a COO matrix every time, but
that conversion is pretty quick.

Although, unless your sparsity pattern doesn't change (which it may not),
> you'll need to zero the entire dense array before reassigning, which will
> also take "a non-negligible amount of time".

Zeroing out a matrix seems to happen very quickly, probably because it's a
vectorized operation taking advantage of the SIMD instructions on modern
processors.  As far as I understand it, allocating huge amounts of memory
requires slower operations.  I did a quick and dirty benchmark, and zeroing
takes a small fraction of the time of allocating.

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