Solve a Diff.equation in another Diff.Equation using ODE

Hello everyone,

I am a novice in programming so please bear with me.

I am currently trying to solve a diff. equation using the ODE45. However, the function that my programm calls for contains a diff.equation itself and is using an ODE23s to solve that one.

I need the ODE45 to use only 1 column of the ODE23s matrix to finish its own process and then hand over both matrices to the script. Simply coupling them does not seem to work.

% Script:

% --- Bunch of Information cutted ---

n = input('...'); % Number of finite elements

tfin = input('...');

tpan = [0 tfin];

tic

[t,x]=ode45('Function_1',tspan,x0);

toc

% Function_1

% --- Bunch of information cutted ---

xdot(1)=(vs*y1(2)-(ls+d)*x(1))/md;

for i=2:nf-1

xdot(i) = (ls*(x(i-1)-x(i))+vs*(y1(i+1)-y1(i)))/m;

y1(i) = a1(i)*x(i)/(1+(a1(i)-1)*x(i));

end

xdot(nf)=(f*xf0+ls*x(nf-1)-lr*x(nf)+vr*y1(nf+1)-vs*y1(nf))/m;

y1(nf) = a1(nf)*x(nf)/(1+(a1(nf)-1)*x(nf));

for i=nf+1:n-1

xdot(i)= (lr*(x(i-1)-x(i))+vr*(y1(i+1)-y1(i)))/m;

y1(i) = a1(i)*x(i)/(1+(a1(i)-1)*x(i));

end

% --- Bunch of information cutted ---

tic

[t,u] = ode23s('Function_2',tspan,t0);

toc

% NOW DO THE FOLLOWING:

% use u(:,n) to calculate xdot(n)

% combine xdot and u to one matrix

% hand over the matrix to script

Can i even expect u and xdot to have the same number of rows just because tspan is the same? I figured the amount of steps taken is depending on the tolerances achieved...

I could probably describe the situation better but I didnt mean to copy a hundred lines of code right from the get go.

Any ideas appreciated.

Best regards

[Torsten]

With the code you posted we can't help you, sorry.

But you can clip your .m-files to your request by using the attachments button under "Insert" in the editor.