lotka.mws

>    deq1:=diff(x(t),t)=a1*x(t)*(1-b1*y(t));deq2:=diff(y(t),t)=a2*y(t)*(x(t)-b2);

deq1 := diff(x(t),t) = a1*x(t)*(1-b1*y(t))

deq2 := diff(y(t),t) = a2*y(t)*(x(t)-b2)

>    with(DEtools):

>    a1:=1; a2:=0.3; b1:=1; b2:=1;

a1 := 1

a2 := .3

b1 := 1

b2 := 1

>   

>    DEplot([deq1,deq2],
[x(t),y(t)],t=-7..7,[[x(0)=1.2,y(0)=1.2],[x(0)=1,y(0)=.7]],stepsize=.2,
title=`Lotka-Volterra model`,color=[.3*y(t)*(x(t)-1),x(t)*(1-y(t)),.1],
linecolor=t/2,arrows=MEDIUM,method=rkf45);

[Maple Plot]

>