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mxSetNzmax (C and Fortran)

Set storage space for nonzero elements

C Syntax

#include "matrix.h"
void mxSetNzmax(mxArray *pm, mwSize nzmax);

Fortran Syntax

subroutine mxSetNzmax(pm, nzmax)
mwPointer pm
mwSize nzmax



Pointer to a sparse mxArray.


Number of elements mxCreateSparse should allocate to hold the arrays pointed to by ir, pr, and pi (if it exists). Set nzmax greater than or equal to the number of nonzero elements in the mxArray, but set it to be less than or equal to the number of rows times the number of columns. If you specify an nzmax value of 0, mxSetNzmax sets the value of nzmax to 1.


Use mxSetNzmax to assign a new value to the nzmax field of the specified sparse mxArray. The nzmax field holds the maximum number of nonzero elements in the sparse mxArray.

The number of elements in the ir, pr, and pi (if it exists) arrays must be equal to nzmax. Therefore, after calling mxSetNzmax, you must change the size of the ir, pr, and pi arrays. To change the size of one of these arrays:

  1. Call mxRealloc with a pointer to the array, setting the size to the new value of nzmax.

  2. Call the appropriate mxSet routine (mxSetIr, mxSetPr, or mxSetPi) to establish the new memory area as the current one.

Ways to determine how large to make nzmax are:

  • Set nzmax equal to or slightly greater than the number of nonzero elements in a sparse mxArray. This approach conserves precious heap space.

  • Make nzmax equal to the total number of elements in an mxArray. This approach eliminates (or, at least reduces) expensive reallocations.


See the following examples in matlabroot/extern/examples/mx.

Introduced before R2006a

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