  p1 = rand(2,1);
  p2 = rand(2,1);
  d = vecnorm ( p1 - p2 );

  hold on;
  plot ( p1(1), p1(2), 'r*' );
  plot ( p2(1), p2(2), 'b*' );
  plot ( [p1(1),p2(1)], [p1(2),p2(2)], 'k-' );
  axis ( 'equal' );
  axis ( [0,1,0,1] );
  hold off;
  grid ( 'on' );
  filename = 'simulate_one.png';
  print ( '-dpng', filename );
  fprintf ( 1, '  Graphics saved as "%s"\n', filename );
 
