Are the values in each compressed column of a sparse matrix stored in order?

If I have a sparse column vector (e.g. a column of a sparse matrix), and I'm accessing the elements of that vector in a mex file, are the row indices guaranteed to be sorted in order, lowest row index first?

Answer 1

[Oliver Woodford]

Since it is possible to write the column data in any order from a mex file, I would say no.

However, I tried three methods of sparse matrix generation:

• sparse(ceil(rand(10000, 1)*1000), ceil(rand(10000, 1)*1000), 1, 1000, 1000)
• sprand(1000, 1000, 0.01)
• sparse(A)

and these all provided sorted columns.