Re: View matrix in CSR / CSC format

[Bård Skaflestad]

On 04/12/15 12:31, Martin Beseda wrote:
> Thank you very much!

You should reply to the mailing list too (and keep your reply below the 
text you're replying to).  That would make it easier for others to 
comment and to point out the mistake I made in my original response. 
Obviously, you don't get the CSC representation by counting the row indices.

I'll atone for that mistake by making the reply more complete.  Here are 
a couple of functions for converting between Octave's sparse matrices 
and the CSR and CSC representations:

    function [ia, ja, sa] = sparse_to_csr(A)
       [ia, ja, sa] = sparse_to_csc(A .');
    end

    function A = csr_to_sparse(ia, ja, sa)
       A = spconvert([expand(ia), ja, sa]);
    endfunction

    function [p, i, x] = sparse_to_csc(A)
       [i, j, x] = find(A);
       p = cumsum([1 ; accumarray(j, 1)]);
    endfunction

    function A = csc_to_sparse(p, i, x)
       A = spconvert([i, expand(p), x]);
    endfunction

    function k = expand(p)
       k = zeros([p(end) - 1, 1]);
       k(p(1 : end - 1)) = 1;

       k = cumsum(k);
    endfunction


Sincerely,
--
Bård Skaflestad <address@hidden>
SINTEF ICT, Applied Mathematics