A = [10 2 -1
    -2 -6 -1
     1 -3 12];
x = [0 0 0]';
b = [5 24.42 36];

G = zeros(3, 3);
f = zeros(1,3);

for i = 1:1:length(b)
    for j = 1:1:length(b)
        if i ~= j
            G(i,j) = -A(i,j) / A(i,i);
        end
    end
    f(i) = b(i)/ A(i,i);
end

for iter = 1:1:10
    xTemp = x;
    for eq = 1:1:length(b)
        x(eq) = G(eq,:) * x + f(eq); 
        %% change "* x" to "* xTemp" to get simple iteration
        %% otherwise it is working as Zeidel Method
    end
end

x;
A * x;
A = A * A
L = zeros(3,3);
for i = 1:1:length(A)
    L(i,i) = sqrt(A(i,i));
    for k = i+1:1:length(A)
        L(k,i) = A(k,i) / L(i,i)
    end
    for j = i+1:1:length(A)
        for k = i:1:length(A)
            L(k,j) = A(k, j) - A(k,i) * A(j,i);
        end
    end
end