What am I doing wrong in my Ode?

Question

Matthew Lozancich 2018-1-11

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https://ww2.mathworks.cn/matlabcentral/answers/376619-what-am-i-doing-wrong-in-my-ode

回答： David Goodmanson 2018-1-11

Can't seem to understand what I'm doing wrong.

function zombie
[t,x]=ode23(@zomb,[0,60],1000)
subplot(2,1,1)
plot(t,x(:,1))
 subplot(2,1,2)
    plot(t,x(:,2))
function dx=zomb(t,x)
mu=0.002;
delta=0.001;
beta=0.002;
gamma=0.0015;
dx=[mu*x(1) - beta*(x(1))*x(2) - delta*(x(1)); -gamma*x(1)*x(2) + beta*x(1)*x(2) - 150*delta*x(2)];
end
end

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Answer 1

David Goodmanson 2018-1-11

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Hi Matthew, you appear to lacking a second initial condition. With one initial condition of 1000, ode23 assumes that x has only one component and so 'zomb' bombs out on the x(2) variable. If you try, e.g.

[t,x]=ode23(@zomb,[0,60],[1000 5])

then it works.