function [yprim]=vander(t, y)
yprim(1)=y(2);
yprim(2)=mu*(1-y(1)^2)*y(2)-y(1);
endfunction

mu=0.4;
n=30; 
xmin=-6; xmax=6;
ymin=-4; ymax=4;
x=linspace(xmin, xmax, n);
y=linspace(ymin, ymax, n);
xbasc();
fchamp(vander,0, x, y, 1, [xmin,ymin,xmax,ymax], "031")
xselect();

m=500; T=30; t=linspace(0,T,m);
couleurs=[21 2 3 4 5 6 19 28 32 9 13 22 18 21 12 30 27];
num=-1;

while %t
  [ci, cx, cy]=xclick();
  if ci==2 then
    break
  else
    plot2d(cx, cy, -9, strf="000")
    y0=[cx; cy];
    y=ode(y0, 0, t, vander);
    num=modulo(num+1, length(couleurs));
    plot2d(y(1,:)', y(2,:)', style=couleurs(num+1), strf="000");
  end
end