Get a pointer to the members of the matrix
M::mtx_item_type* operator M::mtx_item_type*( );
This method returns a contigous "flattened" array containing all the items in the matrix.
Because the pointers are not const, the mtx_flatreader<M> makes a copy of the data contained in the attached matrix, and returns a pointer to the copied data.
Thus the data in the original matrix is never affected by write operations to the passed array.