function [ttot, utot] = rk4(u0, T, n)
y = [];
u = u0;
h = T/n;
y = [y, u0];
m = 0.6;
g = 9.81;
my = 0.2;
L = 1.5;

f = @(t,u) [u(2),-(my/m)*u(2) - (g/L)*sin(u(1))]';

for t=0: h:T

k1 = f(t, u);
k2 = f(t + h/2, u + k1.*(h/2));
k3 = f(t + h/2, u + k2.*(h/2));
k4 = f(t + h, u + k3.*h);

un = u + (k1 + k2.*2 + k3.*2 + k4).*(h/6);

u = un;
y = [y, u];

end
y = y';
t = 0:h:T;
plot(t,y(:,1))
xlabel('Tid')
ylabel('φ')
title('Lösning')
ttot = t';
utot = y;
end