u=@(x,y) 2/3*x-4/3*x.*y;
v=@(x,y) x.*y-y;
range=linspace(0,2,21);
[X, Y]=meshgrid(range,range);
h=quiver(X,Y,u(X,Y),v(X,Y),4);
axis tight
set (h,"linewidth",2)