Set number of rows in array
Call mxSetM to set the number of rows in the specified mxArray. The term rows means the first dimension of an mxArray, regardless of the number of dimensions. Call mxSetN to set the number of columns.
You typically use mxSetM to change the shape of an existing mxArray. The mxSetM function does not allocate or deallocate any space for the pr, pi, ir, or jc arrays. Consequently, if your calls to mxSetM and mxSetN increase the number of elements in the mxArray, enlarge the pr, pi, ir, and/or jc arrays. Call mxRealloc to enlarge them.
If your calls to mxSetM and mxSetN end up reducing the number of elements in the mxArray, you might want to reduce the sizes of the pr, pi, ir, and/or jc arrays in order to use heap space more efficiently. However, reducing the size is not mandatory.
See the following examples in matlabroot/extern/examples/mx.
See the following examples in matlabroot/extern/examples/refbook.