Suppose n is the number of rows (columns) of the matrix. The number of vertical (horizontal) intermediary interpolation points defaults to: 10 if n<20, 5 if 20<n<50, 3 if 50<n<100, and 2 if 100<n. If \INTERPSIZE is used, the first parameter, ntrp, over-rides the defaults and the number of interpolation points in each direction are both set to ntrp.