“…(A possible explanation of such a big difference between the triangular and the full methods may be that the relaxation scheme local error for the full scheme is of order h 12 , h 10 , h 8 for the values, the first and the second derivatives, respectively, while for the triangular scheme this error is of order h 12 , h 8 , h 4 . See Section 6 for results of symbolic calculations.…”