function L = graph_arc_dodecahedron ( )

%*****************************************************************************80
%
%% graph_arc_dodecahedron(): arc list for the dodecahedron graph.
%
%  Discussion:
%
%    There are 20 nodes.
%    There are 30 edges or 60 arcs.
%
%  Licensing:
%
%    This code is distributed under the MIT license. 
%
%  Modified:
%
%    30 April 2026
%
%  Author:
%
%    John Burkardt
%
%  Output:
%
%    integer L(arc_num,2): the arc list.
%
  L = [ ...
     1,  2; ...
     1,  5; ...
     1,  6; ...
     2,  1; ...
     2,  3; ...
     2,  8; ...
     3,  2; ...
     3,  4; ...
     3, 10; ...
     4,  3; ...
     4,  5; ...
     4, 12; ...
     5,  1; ...
     5,  4; ...
     5, 14; ...
     6,  1; ...
     6,  7; ...
     6, 15; ...
     7,  6; ...
     7,  8; ...
     7, 17; ...
     8,  2; ...
     8,  7; ...
     8,  9; ...
     9,  8; ...
     9, 10; ...
     9, 16; ...
    10,  3; ...
    10,  9; ...
    10, 11; ...
    11, 10; ...
    11, 12; ...
    11, 20; ...
    12,  4; ...
    12, 11; ...
    12, 13; ...
    13, 12; ...
    13, 14; ...
    13, 19; ...
    14,  5; ...
    14, 13; ...
    14, 15; ...
    15,  6; ...
    15, 14; ...
    15, 18; ...
    16,  9; ...
    16, 17; ...
    16, 20; ...
    17,  7; ...
    17, 16; ...
    17, 18; ...
    18, 15; ...
    18, 17; ...
    18, 19; ...
    19, 13; ...
    19, 18; ...
    19, 20; ...
    20, 11; ...
    20, 16; ...
    20, 19 ];

  return
end
