function m = main()
  for t=[0:500]
    phi=t/500*2*pi;
    k=1*pi/(2*pi-phi);
    [x,y] = meshgrid(-10:0.5:10);
    [u,v] = fun(x,y,k,phi);
    quiver(x,y,u,v);
    hold on;
    plot(0:10, zeros(1,11) );
    [o,p]=pol2cart((2*pi-phi) * ones(1,11),0:10);
    plot(o,p);
    hold off;
    filename=sprintf('output/%05d.jpg',t);
    print(filename);
  end
end

function [u,v] = fun(x, y, k, phi)
  [l,s] = cart2pol(x,y);
  l=l+2*pi*(l<0);
  u= k .* s.^(k-1) .* (sin(k.*l) .* cos(l) - cos(k.*l).*sin(l)).*(l<=2*pi-phi);
  v= k .* s.^(k-1) .* (sin(k.*l) .* sin(l) + cos(k.*l).*cos(l)).*(l<=2*pi-phi);
end