xlist = linspace ( 0, 4, 201 );
ylist = f123 ( xlist );
plot ( xlist, ylist, xlist, ...
  0*ylist, 'k:', ...
  [ 0.5, 0.5 ], [ -6, 6 ], 'r-', ...
  [ 1.5, 1.5 ], [ -6, 6 ], 'r-', ...
  [ 2.5, 2.5 ], [ -6, 6 ], 'r-', ...
  [ 3.5, 3.5 ], [ -6, 6 ], 'r-', ...
  'LineWidth', 3 )
grid on
xlabel ( '<-- X -->' )
ylabel ( '<-- Y -->' )
title ( 'Fences for y=(x-1)*(x-2)*(x-3)', 'Fontsize', 24 )
print ( '-djpeg', 'f123_fences.jpg' )
