| MATLAB Application Program Interface Reference | Help Desk |
mxSetDimensions
Modify the number of dimensions and/or the size of each dimension
#include "matrix.h" int mxSetDimensions(mxArray *array_ptr, const int *size, int ndims);array_ptr ndims
The desired number of dimensions.
dims
The first element of an array of ints. Each element in the array holds the size of a particular dimension. The first element holds the number of elements in the first dimension (rows); the second element holds the number of elements in the second dimension, and so on.
mxSetDimensions allocates heap space to hold the input size array. So it is possible (though extremely unlikely) that increasing the number of dimensions can cause the system to run out of heap space.
Call mxSetDimensions to reshape an existing mxArray. mxSetDimensions is similar to mxSetM and mxSetN; however, mxSetDimensions provides greater control for reshaping mxArrays that have more than two-dimensions.
mxSetDimensions does not allocate or deallocate any space for the pr or pi arrays. Consequently, if your call to mxSetDimensions increases the number of elements in the mxArray, then you must enlarge the pr (and pi, if it exists) arrays accordingly.
If your call to mxSetDimensions reduces the number of elements in the mxArray, then you can optionally reduce the size of the pr and pi arrays.
Create a populated 3-by-2 mxArray. Then, call mxSetDimensions to expand the mxArray to 4-by-3-by-2. Preserve the original 3-by-2 data as the first page of the expanded mxArray.
#define ROWS 3
#define COLS 2
#define TOTAL_ELEMENTS (ROWS * COLS)
#define NEW_PAGES 4
#define NEW_ROWS 3
#define NEW_COLS 2
#define TOTAL_NEW_ELEMENTS (NEW_PAGES * NEW_ROWS * NEW_COLS)
mxArray *array_ptr;
static double real_data[] = {5.2, 7.8, 4.3, 9.3, 8.2, 7.1};
int new_ndims=3;
int new_dims[3]={NEW_PAGES, NEW_ROWS, NEW_COLS};
double *start_of_new_pr, *start_of_old_pr, *pr;
/* Create a 3-by-2 array named "Apricot" */
array_ptr = mxCreateDoubleMatrix(ROWS, COLS, mxREAL);
pr = mxGetPr(array_ptr);
memcpy((void *)pr,(const void *)real_data,
ROWS*COLS*sizeof(double));
mxSetName(array_ptr, "Apricots");
...
/* Change the dimensions of "Apricots" from 3-by-2 to
4-by-3-by-2. */
mxSetDimensions(array_ptr, new_ndims, new_dims);
/* Allocate space to hold 24 data elements. */
start_of_new_pr = mxCalloc(TOTAL_NEW_ELEMENTS,
sizeof(double));
/* Copy the old real_data to the beginning of the new section. */
start_of_old_pr = mxGetPr(array_ptr);
memcpy(start_of_new_pr, start_of_old_pr, TOTAL_ELEMENTS);
/* Deallocate the space held by the old pr. */
mxFree(start_of_old_pr);
/* Associate the new data section with the array_ptr. */
mxSetPr(array_ptr, start_of_new_pr);
...
For an additional example, see mxSetDimensions.c in the mx subdirectory of the examples directory.
mxGetNumberOfDimensions, mxSetM, mxSetN