function [lvsp] = lvdemo_ode(t,lvs,circs)
  % odefile for multiple vortices
  
  lvsp = zeros(size(lvs));

  for J = 1:length(lvs)
    sum = 0;
    for j = 1:length(lvs)
      if (j ~= J)
          sum = sum + i*circs(j)/2/pi * 1/conj(lvs(J)-lvs(j));
      end
    end
    lvsp(J) = sum;
  end