Can I call another ode45 inside the function file of an ode45 ?

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Anil 2024-2-1

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https://ww2.mathworks.cn/matlabcentral/answers/2077066-can-i-call-another-ode45-inside-the-function-file-of-an-ode45

编辑： Anil 2024-2-19

I have an ode45 function file with equations from a matrix, but few variable in these equations are time dependent and are solutions of other few time dependent coupled equations. Can I use ode45 here to find the solution of these time dependet variables for each time step? I tried to put at the end of the function file (after and before end both ways). But that shows error.

I am giving structure of the function and main file here

%function file

function dvdt=outfun(t,vec)

dvdt=zeros(36,1);

y0=[ 1; 2; 3; 4;]

%alpha and beta are time dependent nonlieanr coupled equations.

[T0 z]= ode45('infun',t0,y0)% can it be t instead of t0?

for ii=1:length(T0)

alpha=z(ii,1);

beta=z(ii,3);

g3r=g*real(alpha)%

g3im=g*imag(alpha)%

g4r=g*real(beta)%

g4im=g*imag(beta)%

a=[.....]%matrix

v=vec;%Initial conditions in the matrix form

N=[n1 n2 n3 n4 n5 n6];

dvrdt= a*v + diag(N) ;% some matrix equations

dvdt(1)=dvrdt(1,1);%equations

....

...

dvdt(36)=dvrdt(6,6);

end

function dydt=infun(t,y)

dydt=zeros(4,1);

dydt(1)= .....;%alpha

dydt(2)=.....;%conj(alpha)

dydt(3)=......;%beta

dydt(4)=......;%conj(beta)

end

%main file

tsapn=0:0.01:10

x=[];

%initial condition

vv=[v11_0, v21_0,v31_0,v41_0,v51_0,v61_0,...

v16_0, v26_0,v36_0,v46_0,v56_0,v66_0];

[T, V]=ode45(@outfun,tspan,vv);% calling

[mm,n]=size(V);

for ii=1:mm

v1=reshape(V(ii,:),6,6);

a=max(eig(v1))

x=[x; T(ii) a]

end

Any suggestions please, thanks. Edit: just modified function names

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Torsten 2024-2-19

编辑：Torsten 2024-2-19

You should state your problem mathematically without code.

My guess is that you don't need two calls to ode45 with 36 and 4 unknowns, respectively, but only one call with 40 unknowns.

Anil 2024-2-19

Dear @Torsten, Thanks for that. That looks much simpler than the earlier complex version. I did that but the only doubt was different equations making me confsued and I went for the two ODE45. Thank you very much @Stephen23 and @Torsten for your help.

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