[Octave-bug-tracker] [bug #53198] nnz could be improved for diagonal matrices

[Dan Sebald]

Follow-up Comment #7, bug #53198 (project octave):

I'll give it a try.  I'm a bit busy this summer, so it may take a while even
though it's not that big of a changeset.

I'm a little confused with the current issorted() for full matrices.  The
following all looks fine:


octave:20> I = [1 1 2]; J = [1 1 2]; SV = [3 4 5];
octave:21> X = sparse (I, J, SV, 3, 4, "unique")
X =

Compressed Column Sparse (rows = 3, cols = 4, nnz = 2 [17%])

  (1, 1) ->  4
  (2, 2) ->  5

octave:22> full(X)
ans =

   4   0   0   0
   0   5   0   0
   0   0   0   0

octave:23> sort(full(X))
ans =

   0   0   0   0
   0   0   0   0
   4   5   0   0

octave:24> sort(full(X),2)
ans =

   0   0   0   4
   0   0   0   5
   0   0   0   0


But why can't issorted() act on a matrix?


octave:25> issorted(sort(full(X)))


I would think that issorted() is a counterpart to sort(), so it should be able
to act on something output by sort().

Furthermore, there is this "rows" option, which refers to sortrows().  Now, I
understand the idea of a sortrows().  It's a vector-based sort that maintains
order across rows; a bit like a spreadsheet sort, if you follow.  But it seems
to me that in order to test whether this is a valid output of sortrows(), one
needs to know how the sorting of sortrows() was done, i.e., the "C" of
sortrows() documentation.  Also, note that this works


octave:30> issorted(sort(full(X)),"rows")
ans = 1


yet without the "rows" it's the error above.  And what about a "cols"
counterpart?  Why should vector-sorting be allowed only in the "rows"
dimension?

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