phase space

[Carlo de Falco]

On 3 Apr 2009, at 14:55, Johannes Wolfgang Woger wrote:

> Hi,
> I am an newby.
>
> How can I obtain a plot of the phase portrait
> of Lotka-Volterra:
>
> octave:92> function xdot = f(x,t)
>> a = 4;
>> b = 4;
>> c = 4;
>> d = 8;
>> E = 1;
>> K = 1;
>> xdot = zeros(2,1);
>> xdot(1) = x(1)*(a-b*x(2)-E*x(1));
>> xdot(2) = x(2)*(d*x(1)-c-K*x(2));
>> endfunction
> octave:93>
> octave:93> t = linspace(0,50,100);
> octave:94> x = lsode("f", [2,1],t);
> octave:95> plot(t,x);
>

plot(x(:,1), x(:,2));
xlabel("x_1");
ylabel("x_2");

but I would suggest using a few more time steps if you want a nice  
looking spiral...

> Thanks

HTH,
c.