Sparse matrix storage in C

Question

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.

Answer 1

Derek, you mentioned in one of the comments that you want to use a single malloc. That means that you know how many nonempty elements you have. Given this, tt is possible to store the sparse matrix in an array which holds, per element, the value of the matrix element and the "location delta" to the next element. Something like:

struct melem {
    int value; // value of data
    int offset; // offset to next element
}

struct melem matrix[num_nonempty_elements];

...

// Note: this is pseudocode!
matrix[row*COLS + col].value = a[row][col];
matrix[row*COLS + col].offset = (row*COLS + col)_[i] - (row*COLS + col)_[i-1];

EDIT: Thinking about it, this is pretty similar to the linked list approach, but requires 1 allocation. OTOH, it may require more calculation to access the required cell.