Homework Set 9 Problem
Let u(x, y) be the solution on 0 x 2 and 0 y 2 of uxx + uyy = 0
with u(0, y) = u(2, y) = u(x, 2) = 0 and u(x, 0) = f (x) the triangular pulse with
f (0) = f (2) = 0 and f (1) = 2.
2x, if 0 x 1;
f (x) =
-2x + 4, if 1 x 2.
Let uj,k = u(j/2, k/2) for j = 1, 2, 3 and k = 1, 2, 3 as obtained by the numerical
method.
(a) Write the linear equations for the 9 unknowns u11 , . . . , u33 in matrix form.
(b) Use symmetry to reduce these to six equations.
(c) Solve the equations to obtain the 9 unknowns u11 , . . . , u33 .
