Saving memory in spones()

[Rik]

5/12/11

The spones() function returns a sparse matrix with a 1 in each non-zero
entry in the matrix.  It is useful for viewing the structure of a matrix,
but obviously all of the actual values are lost.

The code is simple enough to quote in its entirety:

[i, j, v] = find (S);
[m, n] = size (S);

r = sparse (i, j, 1, m, n);

Question: Why not return a sparse logical matrix rather than a sparse
double matrix and save 7 bytes per entry?

r = sparse (i, j, logical (1), m, n);

--Rik