Drexel dragonThe Math ForumDonate to the Math Forum



Search All of the Math Forum:

Views expressed in these public forums are not endorsed by Drexel University or The Math Forum.


Math Forum » Discussions » Software » comp.soft-sys.matlab

Topic: Help with ODE Problem
Replies: 7   Last Post: Jul 23, 2013 12:35 AM

Advanced Search

Back to Topic List Back to Topic List Jump to Tree View Jump to Tree View   Messages: [ Previous | Next ]
Marc

Posts: 108
Registered: 7/2/10
Re: Help with ODE Problem
Posted: Jul 15, 2013 10:38 PM
  Click to see the message monospaced in plain text Plain Text   Click to reply to this topic Reply

"Lauara " <osornol@fiu.edu> wrote in message <ks13gl$pmk$1@newscl01ah.mathworks.com>...
> "Jan Simon" wrote in message <ks0q2f$rla$1@newscl01ah.mathworks.com>...
> > Dear Lauara,
> >
> > Follow the standard approach directly:
> >

> > > Mx??+Cx?+Kx=P(t)
> > > x'' = inv(M) * (P(t) - Cx' -Kx)

> >
> > Lookup table: y1 = x, y2 = x', y3 = x''
> >
> > dydt(1) = y(2);
> > dydt(2) = (P(t) - C * y(2) - K * y(1)) \ M;
> >
> > Or you could expand M to work with the vector y.
> >
> > Kind regards, Jan

>
> Thank you so much Jan for your response. I have written the code as you said:
>
> tspan=[0 0.25 0.5];
> y0=zeros(76,1);
> yp0=zeros(76,1);
> [T,Y]=ode15i(@(t,y) Differential_Equation_Solver(t,y,K,M,C,P),tspan,y0,yp0);
>
> %%%%%%%
>
> function dydt=Differential_Equation_Solver(t,y,K,M,C,P)
> dydt(1) = y(2);
> dydt(2) = M\(P-C*y(2)-K*y(1));
> end
>
> But I am still getting an error for the number of the input arguments:
>
> Too many input arguments.
>
> Error in odearguments (line 88)
> f0 = feval(ode,t0,y0,args{:}); % ODE15I sets args{1} to yp0.
>
> Error in ode15i (line 117)
> [neq, tspan, ntspan, next, t0, tfinal, tdir, y0, f0, ~, odeFcn, ...
>
> Error in Bridge_Displacement (line 49)
> [T,Y]=ode15i(@(t,y) Differential_Equation_Solver(t,y,K,M,C,P),tspan,y0,yp0);
>
> why do you think this format is wrong and how should I fix it?
>
> Again, Thank you very much for your useful tip.


You can not pass the K,M,C,P variables into the solver. See "nested functions" or the documentation on "passing other variables into functions" with the Matlab ODE solvers.

Also, make sure your ode function is spitting on a column vector.

Using the call to dydt = zeros(2,1); before the equations will fix that.

So, your function needs to look like this.....

function dydt = yourODE(t,y)

K = ....
M = ....
etc. etc.

dydt = zeros(2,1);
etc.etc.

end

Try hard coding the variables first, then look into using a nested function.



Point your RSS reader here for a feed of the latest messages in this topic.

[Privacy Policy] [Terms of Use]

© Drexel University 1994-2014. All Rights Reserved.
The Math Forum is a research and educational enterprise of the Drexel University School of Education.