Plotting phase plane from system of second order ODEs

Hi,

I'm using ode45 to solve a system of two second order ODEs (writing it as a system of 4 first order ODEs)

du(1) = u(3); %u'

du(2) = u(4); %v'

du(3) = c*u(3) - (1 - u(1) - a1*u(2))*u(1); %u

du(4) = (c/d)*u(4) - (r/d)*(1- a1*u(1) - u(2))*u(2); %v

I would like to plot a phase plane portrait of two of these (du(1) and du(2)). Is there a way to do this?

Thanks!!

Answer 1

[Star Strider]

See the odeset documentation for Description of Solver Output Properties, particularly for ‘OutputFcn’ and the odephas2 option. That’s the easiest way.

[María Jesús]

Thanks! How about getting direction arrows as well?

[Star Strider]

My pleasure!

For arrows, you will need to use the quiver or quiver3 plot functions. Use the hold function to overplot the arrows on the phase plot.

Sorry for the delay — MATLAB Answers is apparently undergoing some sort of upgrade just now and I didn’t see your reply. It would normally pop to the top of the stack, but didn’t.