here i have an ode system:

diff(x(t),t)=f(x,y,z,w); diff(y(t),t)=g(x,y,z,w);diff(z(t),t)=h(x,y,z,w); diff(w(t),t)=k(x,y,z,w) where f, g, h, k are given nonlinear functions.

Then how can i get the phaseplan of (x(t),y(t))? when i use the procedure of DEplot, it returns an error stating that the DESYS requires two or fewer variables? how can i deal with that?

Any help will be greatly appreciated!

here i have four odes

diff(x(t),t)=f(x,y,z,w); diff(y(t),t)=g(x,y,z,w);diff(z(t),t)=h(x,y,z,w); diff(w(t),t)=k(x,y,z,w)

whrer f,g,h and k are known nonlinear functions? Then how can i get the graph of (x,y)near some point,eg (0,0), by the numeric method? Thank you very much!

Strange thins happens when I choose m=2 and m=3.The whole PDE seems normal and when I let m=2,the maximum is only 12,but when I choose m=3,the maximum goes up to 10^14. This puzzles me.Who can tell me why? How can I get the right answer?  many thanks!

the procedure is as follows:

Hi , every one! Now I use the maple12 and feel it convenient to work with execpt that when I open the procedure by maple10 on another computer, the procedure become messy code? what can I do with this? Is there any direct way to do this without rewrite the procedure?  many thanks!

The concrete procedure is as follows:

PDE := diff(u(x,t),t)+diff(u(x,t),x)=0;  IBC := {u(x,0)=x,u(0,t)=0};

pds := pdsolve(PDE,IBC,numeric,time=t,range=0..0.1);

pds:-plot3d(t = 0 .. .1, x = 0 .. 1, axes = boxed, orientation = [-110, 60], color = [0, 0, u]);

and the greatest number in the graph is over 4,500. I do not understand why the number is so high?  The former PDE and the initial value are very small.   many thanks!