function hand_negation ( )

%*****************************************************************************80
%
%% hand_negation() negates the hand data and shows the result.
%
%  Discussion:
%
%    This program assumes that the file 'hand_data.txt' is available.
%
%  Licensing:
%
%    This code is distributed under the MIT license.
%
%  Modified:
%
%    29 April 2019
%
%  Author:
%
%    John Burkardt
%
%  Reference:
%
%    Cleve Moler,
%    Numerical Computing with MATLAB,
%    SIAM, 2004,
%    ISBN13: 978-0-898716-60-3,
%    LC: QA297.M625. 
%
  fprintf ( 1, '\n' );
  fprintf ( 1, 'hand_negation():\n' );
  fprintf ( 1, '  Negate and plot the hand data.\n' );
%
%  Read the data.
%
  xy = load ( 'hand_data.txt' );
%
%  Make XY an array of column vectors.
%
  xy = xy';
%
%  Repeat the first column at the end so the polygon closes.
%
  xy = [ xy, [ xy(:,1) ] ];
%
%  Define the transformation as a negation matrix.
%
  A = [ -1.0, 0.0; 0.0, -1.0 ];
%
%  Transform the data.
%
  xy2 = A * xy;
%
%  Clear the graphics frame.
%
  clf ( );
  hold ( 'on' );
%
%  Plot the original data.
%
  plot ( xy(1,:), xy(2,:), 'Color', 'r', 'LineWidth', 2 );
%
%  Plot the transformed data.
%
  plot ( xy2(1,:), xy2(2,:), 'Color', 'b', 'LineWidth', 2 );
%
%  Annotate.
%
  axis ( 'equal' );
  grid ( 'on' );
  title ( 'Data (red), and [-1,0;0,-1]*data (blue)', 'fontsize', 16 );

  hold ( 'off' );

  filename = 'hand_negation.png';
  print ( '-dpng', filename );
  fprintf ( 1, '  Graphics saved as "%s"\n', filename );

  return
end
