%---------------------------------------------------------
% 質点の位置の表示
%---------------------------------------------------------
function graph3d(t,q)

  x=q(1:3,:)';
  
  st=num2str(t);
  stitle=strcat('t=',st);
  grid;
  title(stitle);
  xlabel("x")
  ylabel("y")  
  zlabel("z")
  gsplot x with point 1 7