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Bug 1271

Summary: Add view to nonZeros of SparseMatrix
Product: Eigen Reporter: Darcy <darcy>
Component: SparseAssignee: Nobody <eigen.nobody>
Status: CONFIRMED ---    
Severity: Feature Request CC: chtz, darcy, gael.guennebaud
Priority: Normal    
Version: 3.4 (development)   
Hardware: All   
OS: All   
Bug Depends on:    
Bug Blocks: 1104    

Description Darcy 2016-08-05 03:48:23 UTC

The ability to call a method that zeros the coefficients in a sparse matrix.

Currently the setZero() method zeros all allocated memory but it would be nice to set the Aij coefficients to zero, while keeping the row and column arrays allocated and populated.
Comment 1 Gael Guennebaud 2016-08-22 09:04:20 UTC
Exposing a dense "view" on the non-zeros would solve this issue, e.g.:


while enabling many more efficient manipulations on the non zero coefficients. I've suggested this solution several times, e.g. in bug 1104.

Implementing it for compressed matrices is just a matter of returning a 1D dense Eigen::Map. For un-compressed ones, this is much more tricky because we would need to return a list of dense Map for which random access would be extremely inefficient.
Comment 2 Christoph Hertzberg 2016-08-23 12:29:34 UTC
I like the idea of providing a nonZerosView().
If it is to complicated for un-compressed matrices, I think simply restricting this feature to compressed matrices would be ok.
Minor question: Should the return value be a vector or an array? I'm tending towards array, since nonZerosView() would behave more like independent scalars.
Comment 3 Gael Guennebaud 2016-08-23 14:24:49 UTC
I agree with the two suggestions (compressed-only + array).
Comment 4 Gael Guennebaud 2016-08-29 10:08:38 UTC
Done for compressed mode:

Supporting non compressed mode would require a more general expression to concatenate an arbitrary number of vectors/matrices.
Comment 5 Darcy 2016-08-29 10:14:21 UTC
Fantastic, suits my purposes.  Many thanks!
Comment 6 Nobody 2019-12-04 16:05:05 UTC
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