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POSparse matrix storage in C
 

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    <p>I have a sparse matrix that is not symmetric I.E. the sparsity is somewhat random, and I can't count on all the values being a set distance away from the diagonal.</p> <p>However, it is still sparse, and I want to reduce the storage requirement on the matrix. Therefore, I am trying to figure out how to store each row starting at the first non-zero, in order, until I get to the last non-zero. </p> <p>That is, if the first non-zero of row m occurs at column 2, and the last non-zero is at column 89, I want to store in A[m] rows 2-> 89.</p> <p>Since each row does not have the same number of non-zeros, I will make all the rows of A have the same number of elements, and pad zeros to the end of the row for rows that have a smaller number of non-zero elements.</p> <p>How do I do this translation in C? I do not actually have an original, full matrix to just copy the values from (the original matrix is coming to me in CSR form). If I was doing this in fortran, I could just define my array to be two dimensional and just have each row be variable length by tracking the start/stop values of non-zero columns and store it like that. </p> <p>I will try to demonstrate below:</p> <p>This is a matrix representation of the values I know - and for each value, I know the row and column location</p> <pre><code> [1 2 3 4 ] [ 5 6 7 8 ] [ 10 11 12 13 ] m[ 14 15 16 17 18 ] [ 19 20 21 22 ] </code></pre> <p>Now for this one row <code>m</code> has the largest "span" between the first non-zero and last non-zero so my new matrix is going to be <code>5x[span of row m]</code></p> <pre><code> [1 2 3 4 ] [5 6 7 8 ] [10 11 12 13 ] m[14 15 16 17 18] [19 20 21 22 ] </code></pre> <p>As you can see, row <code>m</code> needs no zero padding since it was the longest "span" anyway</p> <p>The other rows now all have row zero as the first non-zero, and maintain the spacing of zeros columns between each non-zero.</p>
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