GaussSeidel(A,b,es,maxit)

function x = GaussSeidel(A,b,es,maxit)
% x = GaussSeidel(A,b):
%   Gauss Seidel method.
% input:
%   A = coefficient matrix
%   b = right hand side vector
%   es = (optional) stop criterion (%) (default = 0.00001)
%   maxit = (optional) max iterations (default = 50)
% output:
%   x = solution vector

if nargin<4, maxit=50; end
if nargin<3, es=0.00001; end
[m,n] = size(A);
if m~=n, error('Matrix A must be square'); end
C = A;
for i = 1:n
  C(i,i) = 0;
  x(i) = 0;
end
x = x';
for i = 1:n
  C(i,1:n) = C(i,1:n)/A(i,i);
end
for i = 1:n
  d(i) = b(i)/A(i,i);
end
iter = 0;
while (1)
  xold = x;
  for i = 1:n
    x(i) = d(i)-C(i,:)*x;
    if x(i) ~= 0
      ea(i) = abs((x(i) - xold(i))/x(i)) * 100;
    end
  end
  iter = iter+1;
  if max(ea)<=es | iter >= maxit, break, end
end
% By Steven C. Chapra