function [ adj, t1_ij ] = hat_monotile_adjacency ( )

%*****************************************************************************80
%
%% hat_monotile_adjacency() returns adjacency information for hat monotile.
%
%  Licensing:
%
%    This code is distributed under the MIT license.
%
%  Modified:
%
%    17 April 2024
%
%  Author:
%
%    John Burkardt
%
%  Output:
%
%    integer ADJ(16,3): ADJ(I,J) describes the J-th neighbor of the 
%    I-th 30-60-90 triangle.  Neighbor J=1 is across from the 30 degree angle,
%    J=2 from the 60 degree angle, and J=3 from the 90 degree angle.
%
%    integer t1_ij(3,2), the (i,j) vertex coordinates of 30-60-90 triangle #1.
%
  adj = [ ...
    -1, -1,  2; ... % 1
    -1,  3,  1; ... % 2
     8,  2,  4; ... % 3
    13,  3, -1; ... % 4
%
    -1, -1,  6; ... % 5
    15,  7,  5; ... % 6
    14,  8,  6; ... % 7
     3, -1,  7; ... % 8
%
    -1, -1, 10; ... % 9
    -1, 11,  9; ... % 10
    -1, 10, 12; ... % 11
    -1, 13, 11; ... % 12
     4, 12, 14; ... % 13
     7, 15, 13; ... % 14
     6, 14, 16; ... % 15
    -1, 15, -1 ];   % 16

  t1_ij = [ ...
    0,  0; ...
    2, -2; ...
    1, -3 ];

  return
end

