function plotf ( a, b, f, color )
%% PLOTF demonstrates how a function name can be an input quantity.
%
%  We could call this function with a statement like:
%
%    plotf ( 0.0, 2.0 * pi, @sin, 'r' );
%
  x = linspace ( a, b, 501 );
  y = f(x);         %  <- We assume the function's name is "f".
  plot ( x, y, 'Linewidth', 3, 'Color', color );
  grid on
  xlabel ( '<-- X -->' );
  ylabel ( '<-- Y -->' );
  title ('I don''t know what function this is!', 'Fontsize', 24 );

  return
end