# 10

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

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

> MODEL := [ ode1, ode2 ] ;

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

>

> DOMAIN := t = 0 .. 1 ;

> WINDOW := x = -3 .. 3,

> y = -3 .. 3 ;

>

> DIRplot := DEplot( MODEL, VAR, DOMAIN, WINDOW, arrows = MEDIUM,

> title = `Direction Field for #10` ):

> DIRplot;

>

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

> PHASEplot := DEplot( MODEL, VAR, DOMAIN, [ IC ], WINDOW,

> arrows=NONE,

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

> title = `Phase Portrait for # 10` ):

> PHASEplot;

>

> IC := [ x(0)=1, y(0)=1 ];

> P1:= DEplot( MODEL, VAR, DOMAIN, [ IC ],

> scene=[ t, x ], arrows=NONE, linecolor=BLUE ):

> P2:= DEplot( MODEL, VAR, DOMAIN, [ IC ],

> scene=[ t, y ], arrows=NONE, linecolor=GREEN ):

> display( [ P1, P2 ] , title = `x and y solution curves for # 10` );

>