Phase Portrait
> ode1 := diff( x(t), t ) = -x(t) - 2*y(t) :
> ode2 := diff( y(t), t ) = x(t) - 4*y(t) :
> MODEL := [ ode1, ode2 ] ;
> VAR := { x(t), y(t) } ;
>
> DOMAIN := t = 0 .. 5 ;
> WINDOW := x = -3 .. 3,
> y = -3 .. 3 ;
>
> IC := [ seq( seq( [x(0)=i/3,y(0)=j ], i=-9..9 ), j=[-3,3] ),
> seq( seq( [x(0)=i, y(0)=j/3], i=[-3,3] ), j=-9..9 ) ];
>
> PHASEplot := DEplot( MODEL, VAR, DOMAIN, WINDOW, IC, arrows = MEDIUM,
> title = `Phase Portrait for #8` ):
> PHASEplot;