function points_plot ( prefix )

%% POINTS_PLOT plots points from a data file.
%
  file_text = sprintf ( '%s.txt', prefix );

  xy = load ( file_text );

  plot ( xy(:,1), xy(:,2), 'b.', 'MarkerSize', 20 );
%
%  Use the same scale on both axes.
% 
  axis equal
%
%  Make the axes just fit the data.
%
  axis tight
%
%  Don't show the axis tick marks and lines.
%
  axis off
%
%  Save the graphics data as a PNG.
%
  file_png = sprintf ( '%s.png', prefix );

  print ( '-dpng', file_png );

  return
end

