Date: Apr 10, 2013 6:26 AM
Author: Torsten
Subject: Re: diff eq
"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.