function L = graph_arc_museum ( )

%*****************************************************************************80
%
%% graph_arc_museum() sets up the arc list for the museum graph.
%
%  Discussion:
%
%    The graph has 18 nodes.
%    The graph has 17 edges and 34 arcs
%.
%    The graph is a tree.
%
%    1   2---3   4---5---6
%    |   |           |
%    7   8---9--10  11--12
%    |   |   |       |   |
%   13--14  15--16--17  18
%    
%  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,  7; ...
    2,  3; ...
    2,  8; ...
    3,  2; ...
    4,  5; ...
    5,  4; ...
    5,  6; ...
    5, 11; ...
    6,  5; ...
    7,  1; ...
    7, 13; ...
    8,  2; ...
    8,  9; ...
    8, 14; ...
    9,  8; ...
    9, 10; ...
    9, 15; ...
   10,  9; ...
   11,  5; ...
   11, 12; ...
   11, 17; ...
   12, 11; ...
   12, 18; ...
   13,  7; ...
   13, 14; ...
   14,  8; ...
   14, 13; ...
   15,  9; ...
   15, 16; ...
   16, 15; ...
   16, 17; ...
   17, 11; ...
   17, 16; ...
   18, 12 ];

  return
end

