c) Phase Plane

> ode1 := diff( x(t), t ) = 2*x(t) + 4*y(t):

> ode2 := diff( y(t), t ) = 3*x(t) + 6*y(t):

> MODEL := { ode1, ode2 };

> VAR := { x(t), y(t) };

>

>

> DOMAIN := t = -1 .. 1 ;

> WINDOW := x = -1 .. 1,

> y = -1 .. 1 ;

> IC := [ seq( seq( [x(0)=i, y(0)=j/3 ], j=-3..3 ), i=[-1,1] ),

> seq( seq( [x(0)=i/3,y(0)=j ], j=[-1,1] ), i=-3..3 ) ];

> PHASEplot := DEplot( MODEL, VAR, DOMAIN, WINDOW, IC, arrows=THIN, arrows = MEDIUM,

> title = `Phase Plane for #18` ):

> PHASEplot;

>