[x,y]=forward_euler(@pendulum_ode,[0,20],[0;3.1],800);
plot(x,y(1,:),'k','linewidth',10)
axis('off')
print -dpng critical_euler.png
[x,y]=rk3(@pendulum_ode,[0,100],[0;3.4642],4000);
plot(x,y(1,:),'k','linewidth',10)
axis('off')
print -dpng critical_rk3.png
