Jacobi method - I obtain the final solution, but the printed intermediary errors are wrong (zeros) ! Some intermediary steps of calculation are wrong or decayed.

% Jacobi method for systems of equations

clc; close all; clear all

n=4;    % INPUT
A=[6 2 1 2  ;   2 5 -1 1  ;   1 -1 5 -1  ;   2 1 -1 7];
b=[5 ; -16.5 ; 23.5 ; -1.5];


x0 = zeros(1,n);    %intitial guess x0= all values are zero
xold=zeros(1,n);
x = [x0]';
       itr=0;       
       err=1; errmax=0.001;    itrmax=100;
        
while (max(err)>errmax) & (itr<itrmax)
                         itr=itr+1;
                     k(itr)=itr;
                                        xold=x;     %(itr,i)
    for i = 1:n
                                                                    sigma = 0; %used to sum the values for each row of the A-matrix 

        for j = 1:n

            
            if j~=i     %coef. from the diag. it is omitted from the sum

                sigma = sigma + A(i,j)*xold(j);

            end

        end
            
                x (i)= (b(i)-sigma)/A(i,i); %x_i is calc. from the eq. and recorded for each iter.
                xnew(i)=x(i);
                                                                err=abs(xold-x);

               %x(i)=x;
                               %err(i)=err;
                                x(itr,i)=x(i);
                xold(itr,i)=xold(i);
                err(itr,i)=err(i);
    end
end

disp(' -----OUTPUT-----')

table(x(:,1),x(:,2),x(:,3),x(:,4),'VariableNames', {'x_1','x_2','x_3', 'x_4'})

table(xold(:,1),xold(:,2),xold(:,3),xold(:,4),'VariableNames', {'xold_1','xold_2','xold_3', 'xold_4'})

table(err(:,1),err(:,2),err(:,3),err(:,4),'VariableNames', { 'err_1','err_2','err_3', 'err_4'})

table(k(:), x(:,1),x(:,2),x(:,3),x(:,4),...
    xold(:,1),xold(:,2),xold(:,3),xold(:,4),  err(:,1),err(:,2),err(:,3),err(:,4),'VariableNames',...
    {'k','x_1','x_2','x_3', 'x_4',  'xold_1','xold_2','xold_3', 'xold_4',   'err_1','err_2','err_3', 'err_4'})