ODE Phase Portrait and MATLAB: Get pplane !!

I notice many hits to this blog are from people searching for things like "phase portrait matlab".

For those who are looking for help drawing nonlinear phase portraits of ODE systems in MATLAB, I recommend you check out pplane and dfield.

Here's a review of dfield and pplane that gives some screen shots.

I've not used dfield, but I've used pplane a lot. It's a great tool (in new versions of MATLAB, it's a single script file) that gives a GUI frontend to plot nonlinear ODE phase portraits. It then allows you to find their equilibrium points and plot trajectories as well as a number of other fun things. For example, you can Jacobian linearize a system around and equilibrium point and it will give you the linear phase portrait as well as the eigenvalues of the linearlized system and a set of normalized eigenvectors.

Lots of course web pages use pplane (specifically pplane6, for MATLAB6.x). I recommend you download the software and search for pplane or pplane6 if you want more information. However, it's VERY EASY TO USE, so I don't think you'll need much help.