[Octave-bug-tracker] [bug #45622] Sparsity of sparse matrix when assigning all elements

[Amro]

Follow-up Comment #2, bug #45622 (project octave):

Interesting, I didn't know about the "sparse_auto_mutate" option!

As for your interpretation of the expression M(:), I'm not sure it applies to
MATLAB, it being similar in behavior to REPMAT...


M = sparse(4,4);
M(:) = sparse(1);


The above is no different from the previous code with "M(:) = 1" when run in
MATLAB.

As for mixing different data types, there are well-defined rules for
up/down-casting between unlike classes, as described in this documentation
page:

http://www.mathworks.com/help/matlab/matlab_prog/valid-combinations-of-unlike-classes.html


M = uint8 (zeros (2,2));
M(:) = 1.1;


So according to the previous link, the matrix stays uint8 as expected, and the
1.1 elements are basically rounded to 1, i.e equivalent to writing "M(:) =
uint8(1.1)". I view sparsity as an attribute of the array not a data type on
its own.

The way I see it, "M(:) = ..." is simply treated as a special case in MATLAB,
and the sparse matrix gets converted to full unless the scalar value 0 is used
as in "A(:)=0".

I'm not necessarily asking to reproduce the behavior in Octave... Personally I
think a sparse matrix should remain so no matter what operation is performed
on it, excluding of course explicit conversion to FULL.


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