Apply the program to the square grid in 0 ≤ x ≤ 5, 0 ≤ y ≤ 5 with h = 1 and u = 220 on the upper and lower edges, u = 110 on the left edge and u = -10 on the right edge. Solve the linear system also by Gauss elimination. What accuracy is reached in the 20th Gauss–Seidel step?