[Maxima] Problems with plotdf

S. Newhouse sen1 at math.msu.edu
Fri Jun 20 14:58:55 CDT 2008


Richard Hennessy wrote:
> Actually I think I meant if the diff eq was
>
> 'diff(y,x,2)+x^2*y=e*y
>
> 'diff(y,x,2)+x^4*y=e*y
>
> I want to see the direction field of de/dx if that is possible.
>
> Rich
>
>
I don't understand your ODE. Is e supposed to be a function of x?

Also, even if e were a constant, you have a second order equation with 
independent variable x and dependent variable y, and writing (say the 
second one ) as
y'' = e^y - x^4*y

to do 'direction fields' you would have to write it as three dimensional 
system and take short line segments in the directions of the associated 
vector field. The routine plotdf only works with 2d autonomous systems. 
This includes the case of first order 1d non-autonomous systems, since 
they can be made into 2d autonomous systems.

-sen


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