Problems with a simple system of ODE

[Freidenker]

Hello,

I have a simple system of ODE;

function xdot=test(t,x);

xdot=[
2*x(1)*(1-x(1)/2000)-(15*x(1)*x(2))/(x(1)+70);
1*x(2)*((15*x(1))/(x(1)+70)-9)];

return;

tspan=[0 50]; x0=[1000;20];
options=odeset('RelTol',0.01);

[t,x]=ode23('test',tspan,x0,options);

plot(t,x, '-')

xlabel('time');
ylabel('size');

As you can see, the RelTol is very high, still, I can't plot this, it says "busy" and it waits, waits, waits... nothing happens. I really can't understand, it's a simple system !

BTW, how can I put all the programs in a single m file ?

Thank you,

 

[xnuke]

You're only putting in two time points, 0 and 50. Change the tspan line to tspan=linspace(0,50,10000); x0=[1000;20]; and try it again.

Also, the way the ODE solvers work is you put the ODE equation in a separate m-file function, then call that function. I don't know how to put everything in the same file; maybe someone else knows.

xnuke
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