%This file delines the flow field for computation of Lagrangian variables.
function yprime=lagvort(t,y);
global eps om;
yprime=[y(2)/(y(2)^2+(y(1)-eps*cos(om*t))^2)
   -(y(1)-eps*cos(om*t))/(y(2)^2+(y(1)-eps*cos(om*t))^2)];