[Octave-bug-tracker] [bug #58215] sparse multiplication with Inf

[Rik]

Follow-up Comment #6, bug #58215 (project octave):

I agree that the fact that the end result depends on the representation is not
a good result.  The user shouldn't have to understand that a full, diagonal,
or sparse matrix representation is being used when they contemplate
multiplying two variables.

For the moment we can set aside diagonal matrices which Matlab doesn't
implement (it just uses full matrices even for diag matrices).

Here is a table of possibilities showing the various outcomes:


full scalar * full matrix   : IEEE rules
full matrix * full matrix   : IEEE rules
full scalar * sparse matrix : IEEE rules (Matlab only)
sparse scalar * sparse matrix : IEEE rules (Matlab only)
sparse matrix * sparse matrix : ! IEEE rules 


I'm not a big user of sparse matrices so I don't understand why you would want
to have an exception if one of the arguments is a scalar.  I can understand
why you would want to have different rules for sparse matrix by sparse matrix
multiplication because it does simplify the algorithm.  I guess what I would
want to know is how many practitioners who regularly use sparse matrices would
find strict implementation of IEEE rules useful.  My guess is that most
algorithms have been developed assuming the current behavior and so it
wouldn't be particularly useful. 


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