Why the code gives an error?

Hi I am getting the following error in the code shown below:

function[X] = gauss_seidel(A,b)
N = length(b);
X = zeros(N,1);
err = 1;
while err>0.001
  for i =1:1:N
      sum = 0;
      for j = 1:1:N
          if j~=i
              sum = sum+A(i,j)*X(j,1);
          end
      end
      X(i,1) = (b(i,1)-sum)/A(i,i);
  end
  Z = A*X-b;
  d = sum(Z);
  err = abs(d);
end

and the error is:

>> gauss_seidel(A,b)

??? Subscript indices must either be real positive integers or logicals.

Error in ==> gauss_seidel at 16

d = sum(Z);

I don't know why this error is happening here.

Answer 1

[Azzi Abdelmalek]

You are using sum as a variable, and as a function in

sum = sum+A(i,j)*X(j,1);
d = sum(Z);

[Caped Crusader]

Thanks, I failed to notice it.