“…, (14) f (x, y, t) = 1 + 2 f 2 (x, y, t) + 4 f 4 (x, y, t) + ..., (15) h(x, y, t) = 1 + 2 h 2 (x, y, t) + 4 h 4 (x, y, t) + ..., (16) where g j , ( j = 1, 3, 5, ...) are the complex functions of x, y and t, and f n , h n , (n = 2, 4, 6, ...) are the real ones. Substituting expression ( 14)-( 16) into ( 9)- (11) and collecting the coefficients of the same power of , we have from Eq. ( 9)…”