A = [
    1 0 -1 0 0 0 0
    -1 1 1 0 0 0 0
    0 -1 2 -1 0 0 0
    0 -1 0 2 0 1 0
    0 -1 -1 0 2 1 1
    0 0 1 -1 0 2 -1
    0 0 0 -1 1 -1 2
];

b = [0 0 0 0 0 20 0]';

prog = 1e-6;
max_iter = 500;
t0 = b;
lambda_all = [];
lambda = (norm(t0, inf)/max(abs(t0)));

 for i = 1:max_iter
    t1 = A*t0;
    lambda1 = (norm(t1, inf)/max(abs(t0)));
    lambda_all = [lambda_all lambda1];
    if(abs(lambda1-lambda) < prog)
       i = max_iter;
       tend = (t1 /(norm(t1,inf)))
    end
    i = i+1;
    lambda = lambda1;
    t0 = t1
 end

figure(1)
plot(lambda_all)