MATLAB: Index in position 2 exceeds array bounds(must not exceed 3), why am i getting this error

gauss seidal

A=[15 6 3;2 11 -3;5 -2 9];
B=[16;5;8];
P=[0;0;0];
Max=100;
disp('Gauss Seidal Method');
disp('x1 x2 x3')
for k=1:max
    for j=1:n
        if (j==1)
        x(1)=(B(1)-A(1,2:n)*P(2:n))/A(1,1);
        else if(j==n)
        x(n)=(B(n)-A(n,1:n-1)*(x(1:n-1))')/A(n,n);    
        else
        x(j)=(B(j)-A(j,1:j-1)*x(1:j-1)'-A(j,j+1:n)*P(j+1:n))/A(j,j);
        end
        end
    end
    disp([x(1) x(2) x(3)])
    err=abs(norm(x'-P));
    P=x';
    if err<0.00001
       break
    end
end
    disp('solution is:')
    disp([x(1) x(2) x(3)])

Best Answer

A=[15 6 3;2 11 -3;5 -2 9];
B=[16;5;8];
P=[0;0;0];
Max=100;
[m,n] = size(A) ;
disp('Gauss Seidal Method');
disp('x1 x2 x3')
for k=1:Max
    for j=1:n
        if (j==1)
        x(1)=(B(1)-A(1,2:n)*P(2:n))/A(1,1);
        else if(j==n)
        x(n)=(B(n)-A(n,1:n-1)*(x(1:n-1))')/A(n,n);    
        else
        x(j)=(B(j)-A(j,1:j-1)*x(1:j-1)'-A(j,j+1:n)*P(j+1:n))/A(j,j);
        end
        end
    end
    disp([x(1) x(2) x(3)])
    err=abs(norm(x'-P));
    P=x';
    if err<0.00001
       break
    end
end
disp('solution is:')
disp([x(1) x(2) x(3)])
Check the solution:
sol = A\B
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