Help me to fix it because the error said Attempted to access xnew(2); index out of bounds because numel(xnew)=1. Error in jacobi (line 22) err = norm(xnew(​i)-x(i),In​f)/norm(xn​ew(i),Inf)​;

a = [1, 0, -1; -1/2, 1, -1/4;1, -1/2, 1];
b = [0.2; -1.425; 2];
n = length(b);
x = zeros(n,1);
xnew = zeros(n,1);

x(:) = 0;
iterlimit = 3;
tol = 0.001;

for iteration = 1 : iterlimit
    convergence = true;
    for i=1 : n %loop of equtions
        sum = 0;
        for j = 1: n % loop of summation
            if j~= i
                sum = sum + a(i,j) * x(j)
            end;
        end;
        xnew = -(1/a(i,i)) * (sum - b(i));

          err = norm(xnew(i)-x(i),Inf)/norm(xnew(i),Inf);
          if err <0 tol
              convergence = false;
          end;  
      end;
      if convergence
          break
      end
      x = xnew;
  end;
  disp('iteration: ')
  iter
  disp('solution: ')
  xnew

Answer 1

[Torsten]

In the line

xnew = -(1/a(i,i)) * (sum - b(i));

you reset xnew from a (3x1) vector to a scalar. That's the reason why for i=2 the element xnew(2) no longer exists.

Best wishes

Torsten.