Date: Apr 10, 2013 6:16 AM
Author: Guest
Subject: Re: diff eq
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