%---------------------------------------------------------
% 渦点の位置の表示
%---------------------------------------------------------
function graph(t,z)

  x=z(1,:);
  y=z(2,:);
  st=num2str(t);
  stitle=strcat('t=',st);
  axis([-2,2,-2,2],"equal")
  grid;
  title(stitle);
  xlabel("x")
  ylabel("y")  
  plot(x,y,"@32");