Error in ode45

[Maurício Melo Câmara]

Hi!

I'm trying to solve a system of ODE's with:

[t,y] = ode45('myfun', span, yo)

where 'myfun' declares a function in the form y' = f(t,x), and 'myfun' is in the same folder where the file calling ode45 is, but Octave is returning the following error:

error: First input argument must be a valid function handle

error: called from: /home/octave/odepkg-0.8.0/ode45.m at line 62, column 5

Isn't 'myfun' in the command above a valid function handle?
I'm still not able to solve this problem.
Could anyone help me?

Thanks.