What is the memory cost for multiplying sparse matrices? It seems to be much larger than the memory used by either of the matrices being multiplied:
>> A = sprand(5e9,2, 1e-7); B = sparse(eye(2));
Name Size Bytes Class Attributes
A 5000000000x2 16024 double sparse
B 2x2 56 double sparse
Error using *
Out of memory. Type HELP MEMORY for your options.
As you can see in the example above, the sparse matrices A and B are not taking up much memory, but computing A*B still results in an out of memory error. Why does this happen, and is there a way to avoid it?