(c) -- Phase Portrait

> IC := seq( seq( [x(0)=i/2, y(0)=j/2], j=-3..3 ), i=-3..3 );

> DEplot( MODEL, VAR, DOMAIN, [ IC ], WINDOW,

> scene=[ x, y ], arrows=MEDIUM, linecolor=BLUE,

> title = `Phase Portrait for # 16` );

Notice how the curves at different radii have different lengths. All solution curves are circles, but the common term in each ODE increases the "speed" of the solution as the distance from the unit circle increases.

>