[问题] 应用Runge_kutta法的程序怎么改正？

[guozhiping]

请大家帮我看一下错误在哪里，我找不出来：

function dydt=vdp1(t,y)
dydt=[y(2);(1-y(1)^2)*y(2)-y(1)];
[t,y]=ode23(@vdp1,[0 20],[0 -0.5]);
% plot(t,y(:,1));



??? function dydt=vdp1(t,y)
|
Error: Function definitions are not permitted at the prompt or in scripts.