Search All of the Math Forum:
Views expressed in these public forums are not endorsed by
Drexel University or The Math Forum.


Torsten
Posts:
1,604
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.



