Problem using ode23tb (Error: Index exceeds the number of array elements)

Hello

I am trying to use the function ode23tb to solve the system of ODEs described bellow. However, I am having trouble, because the function returns an error, namely "Index exceeds the number of array elements (1)". I am not sure which variable is causing the problem. I am indexing the argument y within f, but, as far as I can understand, the same thing is done in the vdp1000 example in the ode23tb documentation and it causes no trouble. Thanks in advance for your help.

VDD = 10;
Ld = 120e-6;
Cg = 50e-12;
Cb = 40e-12;
RS = 50;
RL = 6.6;

iD = @(vG,vD) 10*(1/2.*(vG-3)+1/20.*log(2*cosh(10*(vG-3)))).*(1+0.003.*vD).*tanh(vD);

f = @(y,vs)[
    1/Cg*((vs-y(1))/RS-iD(y(1),y(2))-y(3)-y(2)/RL);
    1/Cg*(vs-y(1))/RS-(Cb+Cg)/(Cb*Cg)*(iD(y(1),y(2))+y(3)+y(2)/RL);
    (y(2)-VDD)/Ld;
];

ff = @(y,t) f(y,3+20*sin(2*pi*10e6*t));

[t,y] = ode23tb(ff,[0 pi/(10e6*pi)],[3; 10; 10/6.6]);

Answer 1

[Alan Stevens]

Must be something to do with the nested functions! It works when structured as follows:

[t,y] = ode23tb(@yfn,[0 pi/(10e6*pi)],[3; 10; 10/6.6]);

plot(t,y),grid

function dydt = yfn(t,y)
        VDD = 10;
        Ld = 120e-6;
        Cg = 50e-12;
        Cb = 40e-12;
        RS = 50;
        RL = 6.6;
        
        vG = y(1); vD = y(2);
        iD = 10*(1/2.*(vG-3)+1/20.*log(2*cosh(10*(vG-3)))).*(1+0.003.*vD).*tanh(vD);
        vs = 3+20*sin(2*pi*10e6*t);
        dydt = [1/Cg*((vs-y(1))/RS-iD-y(3)-y(2)/RL);
               1/Cg*(vs-y(1))/RS-(Cb+Cg)/(Cb*Cg)*(iD+y(3)+y(2)/RL);
               (y(2)-VDD)/Ld];      

end

(Not clear why you have pi/(constant*pi) as the pi's will cancel each other).

[José Filipe]

It worked indeed! Thank you very much!