Zeit = [0 1 2 3 4 5 6];
u_2 = [2.09 2.09 2.4012 2.4012 2.7858 2.7858 2.8474];
u_4 = [0 4.1564 4.1564 4.8222 4.8222 4.9288 4.9288];

plot(Zeit,u_2,'b','linewidth',2);
grid on;
hold on;
plot(Zeit,u_4,'r','linewidth',2);
axis([0 7 0 6]);