function xder = vander(t,x)
xder1 = x(2)
xder2 = x(2).*(1-x(1).^2)-x(1)
xder(1,1) = xder1;
xder(2,1) = xder2;
%xder = [x(2);x(2).*(1-x(1).^2)-x(1)]