function book_filter ( )

  n = 11;
  c = - log ( 2.0 );
  t = linspace ( 0, 10, n );
  e = 1024 * exp ( c * t );

  clf ( );
  hold ( 'on' );
  plot ( t, e, 'r-', 'linewidth', 3 );
  plot ( t, e, 'k.', 'markersize', 30 );
  hold ( 'off' );
  grid ( 'on' );
  xlabel ( '<-- T -->' );
  ylabel ( '<-- E(T) -->' );
  title ( 'Error decay after repeated proofreading' );
  filename = 'book_filter.png';
  print ( '-dpng', filename );
  fprintf ( 1, '  Graphics saved as "%s"\n', filename );

  pause ( 5 );

  return
end

