> restart:with(plots):
> R:=proc(x,y);
> d1:={diff(u(t),t)=v(t),
diff(v(t),t)=-(x+y*cos(t))*u(t), u(0)=1, v(0)=0};
> a:=dsolve(d1,{u(t),v(t)},
type=numeric, method=dverk78, output=listprocedure);
> d2:={diff(u(t),t)=v(t),
diff(v(t),t)=-(x+y*cos(t))*u(t), u(0)=0, v(0)=1};
> b:=dsolve(d2,{u(t),v(t)},
type=numeric, method=dverk78, output=listprocedure);
> T:=subs(a,u(t))+subs(b,v(t));
P:=evalf(T(2*Pi));
> end proc;
> contourplot(R,-0.5..10,-2..2, filled=true, contours=[-2,2], grid=[20,20],coloring=[yellow,red]); Et voici le résultatPS: Si vous souhaitez un tracé plus précis, vous pouvez augmenter le nombre de points (commande: grid= ), ou le domaine du tracé...