Search All of the Math Forum:

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

Topic: diff eq
Replies: 8   Last Post: Apr 11, 2013 2:27 AM

 Messages: [ Previous | Next ]
 Torsten Posts: 1,639 Registered: 11/8/10
Re: diff eq
Posted: Apr 10, 2013 6:26 AM

"richard " <richard7893@embarqmail.com> wrote in message <kk3e55\$lbv\$1@newscl01ah.mathworks.com>...
> Hello
>
> I am doing as you posted and calling ode45 from a different mfile. In my code I am really using a's instead of x's, does that cause a problem?
>
> So when I run the first file which is this:
> function da = system_ex(t,a)
> da(1) = -2.4712*a(1) + 0.005*a(2) + 0.56*a(3)+ 0.1*a(4);
> da(2) = 0.385*a(1) - 0.1002*a(2)
> da(3) = 0.002*a(2) - 0.6462*a(3)
> da(4) = 0.007*a(2) - 0.2042*a(4)
> It is still saying input argument 'a' is undefined.
>
> but the a(t) is what I am trying to find. In a way I think I'm defining 'a' with this file, what's wrong with this part?
>
> and for my second mfile, when I am calling ode45 it wont run probably due to 'a' function being undefined
> "Bruno Luong" <b.luong@fogale.findmycountry> wrote in message <kjtnkm\$ro7\$1@newscl01ah.mathworks.com>...

> > "richard " <richard7893@embarqmail.com> wrote in message <kjrsih\$mgb\$1@newscl01ah.mathworks.com>...
> >

> > >
> > > this is what I am typing into MATLAB:
> > > function dx = system_ex(t,x)
> > > dx = zeros(4,1);
> > > dx(1) = -2.4712*x(1) + 0.005*x(2) + 0.56*x(3)+ 0.1*x(4);
> > > dx(2) = 0.385*x(1) - 0.1002*x(2)
> > > dx(3) = 0.002*x(2) - 0.6462*x(3)
> > > dx(4) = 0.007*a(2) - 0.2042*x(4)
> > > [T,X] = ode45(@systems_ex,[0 10],[1 0 0 0])
> > > plot(t,x(:,1))
> > >

> >
> > I hope you save system_ex in an mfile and call ode45 on another mfile. You seem to put everything in the same mfile.
> >
> > Bruno

Start from example 1 under
http://www.mathworks.de/de/help/matlab/ref/ode23.html
and see whether it works.
Then replace the relevant parts step by step.

Best wishes
Torsten.

Date Subject Author
4/7/13 Guest
4/8/13 Bruno Luong
4/10/13 Guest
4/10/13 Torsten
4/10/13 Guest
4/10/13 Torsten
4/10/13 Bart
4/11/13 Torsten
4/10/13 richard