function e = edge_hexiamond ( index )

%*****************************************************************************80
%
%% edge_hexiamond() returns the edge list defining a given hexiamond.
%
%  Discussion:
%
%    The edge list contains the sequence of parallelogram IJ coordinates
%    of the nodes that lie on the boundary of the polyiamond, listed
%    in counterclockwise order.
%
%  Licensing:
%
%    This code is distributed under the MIT license.
%
%  Modified:
%
%    06 November 2020
%
%  Author:
%
%    John Burkardt
%
%  Input:
%
%    integer INDEX, a value between 1 and 12.
%
%  Output:
%
%    integer E(EN,2): the (I,J) parallelogram point coordinates
%    of the vertices that lie on the boundary of the hexiamond.
%

%
%  bat/chevron
% 
 if ( index == 1 )
    e = [ ... 
      0, 0; ...
      1, 0; ...
      2, 0; ...
      2, 1; ...
      2, 2; ...
      1, 2; ...
      1, 1; ...
      0, 1 ];
%
%  butterfly
%
  elseif ( index == 2 )
    e = [ ... 
      1, 0; ...
      2, 0; ...
      3, 0; ...
      2, 1; ...
      2, 2; ...
      1, 2; ...
      0, 2; ...
      1, 1 ];
%
%  club/crook
%
  elseif ( index == 3 )
    e = [ ... 
      1, 0; ...
      2, 0; ...
      3, 0; ...
      3, 1; ...
      2, 1; ...
      1, 1; ...
      0, 2; ...
      0, 1 ];
%
%  crown
%
  elseif ( index == 4 )
    e = [ ... 
      1, 0; ...
      2, 0; ...
      3, 0; ...
      3, 1; ...
      2, 1; ...
      1, 2; ...
      1, 1; ...
      0, 1 ];
%
%  hexagon
%
  elseif ( index == 5 )
    e = [ ... 
      1, 0; ...
      2, 0; ...
      2, 1; ...
      1, 2; ...
      0, 2; ...
      0, 1 ];
%
%  lobster
%
  elseif ( index == 6 )
    e = [ ... 
      1, 0; ...
      1, 1; ...
      2, 0; ...
      2, 1; ...
      1, 2; ...
      0, 3; ...
      0, 2; ...
      0, 1 ];
%
%  pistol/signpost
%
  elseif ( index == 7 )
    e = [ ... 
      1, 0; ...
      1, 1; ...
      2, 1; ...
      2, 2; ...
      1, 2; ...
      0, 3; ...
      0, 2; ...
      0, 1 ];
%
%  rhomboid/bar
%
  elseif ( index == 8 )
    e = [ ... 
      0, 0; ...
      1, 0; ...
      2, 0; ...
      3, 0; ...
      3, 1; ...
      2, 1; ...
      1, 1; ...
      0, 1 ];
%
%  shoe/hook
%
  elseif ( index == 9 )
    e = [ ... 
      0, 0; ...
      1, 0; ...
      1, 1; ...
      2, 0; ...
      2, 1; ...
      1, 2; ...
      0, 2 ;
      0, 1 ];
%
%  snake
%
  elseif ( index == 10 )
    e = [ ... 
      1, 0; ...
      1, 1; ...
      2, 1; ...
      2, 2; ...
      1, 3; ...
      1, 2; ...
      0, 2; ...
      0, 1 ];
%
%  sphinx
%
  elseif ( index == 11 )
    e = [ ... 
      0, 0; ...
      1, 0; ...
      2, 0; ...
      3, 0; ...
      2, 1; ...
      1, 1; ...
      0, 2; ...
      0, 1 ];
%
%  yacht
%
  elseif ( index == 12 )
    e = [ ... 
      0, 0; ...
      1, 0; ...
      2, 0; ...
      2, 1; ...
      1, 2; ...
      1, 1; ...
      0, 2; ...
      0, 1 ];
  else
    e = [];
  end

  return
end

