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

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Oliver Woodford
Oliver Woodford on 20 Nov 2015
Answered: Oliver Woodford on 20 Nov 2015
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?

Answers (1)

Oliver Woodford
Oliver Woodford on 20 Nov 2015
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.

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