why i am getting weird results when giving input as a chirp signal ?

Hello,

I am doing simulation with chirp signal. I am giving chirp signal as an external input to adaptive hopf oscillator.

first time i have set F0 = 100 hz and F1 = 400 hz and for 0 to 20 secs i have simulated. The initial condition i have given for hopf oscillator frequency is 90 hz ... ok results are satisfactory but when i am changing parameters like starting frequency or target frequency or simulation time ... results are changing.. for example if i am giving F0 = 100 hz and F1 = 300 hz then the graph is showing some weird results. Its not adapting frequency. why this is happening ? its not adapting frequency when parameter change ...

the folloing is my code ...

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Tspan= 0:0.001:20; % time vector

f0=100;

f1=400;

fi = chirp(Tspan,f0,20,f1,'linear');

ti=Tspan;

[T,Y]=ode45(@(t,y) myeqd1(t,y,ti,fi),Tspan,[1;1;90]);

plot (T,Y(:,3));

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function

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function dz = myeqd1(t,y,ti,fi)

dz = zeros(3,1);

mu=0.3;

r= sqrt(y(1)^2 + y(2)^2);

K=500;

F=interp1(ti,fi,t);

dz(1)= (mu - r^2)*y(1) - y(3)*y(2) +K*F;

dz(2) = (mu - r^2)*y(2) + y(3)*y(1);

dz(3) = (-K*F) * (y(2)/sqrt(y(1)^2 + y(2)^2));

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The following figure showing for F0=100, F1 = 400 for Timespan is 20 secs...the graph showing it is going from 90hz (initial value) to adapted value 400 hz

but the second fugure shows for F0=100 and F1= 300 and simulation time is 20 secs.... the graph is going from 90 hz (initial value) to some wierd value above 1800 hz .