De-allocation un-used spalloc

Hi

For the S = spalloc(m,n,nz); function where users can pre-allocate non-zero elements, I wonder if there's a way to de-allocate unused elements. For example S = spalloc( 100000, 500, 2e6); and I only allocate 1e6 element. Is there away to shrink down S to only 1e6 elements?

Thanks

Answer 1

[Jan]

I'd try it by:

S = spalloc( 100000, 500, 2e6);
... fill in 1e6 values
T = spalloc( 100000, 500, 1e6);
T = S;

Inside the mex level you could use mxRealloc to shrink the reserved block of memory for the data and indices, but even then it is not guaranteed, that the same start address is used or that the free'd part of the memory is given back to the operating system directly or later. Therefore I assume the creation of a new smaller array and copy of the values is not very much worse. But if you are very low on memory, the temporary creation of another array is a problem.

Answer 2

[Pete sherer]

Also would nnz() or numel() provide actual #elements used?

[Jan]

Please do not post new questions in the section for answers.

You can simply try it. nnz counts the non-zero values, while numel concerns the number of elements or the full matrix.