function [ adj, t1_ij ] = tile180_adjacency ( )

%*****************************************************************************80
%
%% tile180_adjacency() returns adjacency information for tile 180.
%
%  Licensing:
%
%    This code is distributed under the MIT license.
%
%  Modified:
%
%    24 February 2021
%
%  Author:
%
%    John Burkardt
%
%  Output:
%
%    integer ADJ(36,3): 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 = [ ...
     2, 20,  6; ... % 1
     1, 19,  3; ... % 2
     4,  8,  2; ... % 3
     3,  7,  5; ... % 4
     6, -1,  4; ... % 5
     5, -1,  1; ... % 6
%
     8,  4, 12; ... % 7
     7,  3,  9; ... % 8
    10, -1,  8; ... % 9
     9, 33, 11; ... % 10
    12, 23, 10; ... % 11
    11, 22,  7; ... % 12
%
    14, 36, 18; ... % 13
    13, -1, 15; ... % 14
    16, 28, 14; ... % 15
    15, 29, 17; ... % 16
    18, 25, 16; ... % 17
    17, 26, 13; ... % 18
%
    20,  2, -1; ... % 19
    19,  1, 21; ... % 20
    -1, -1, 20; ... % 21
%
    23, 12, -1; ... % 22
    22, 11, 24; ... % 23
    -1, 27, 23; ... % 24
%
    26, 17, -1; ... % 25
    25, 18, 27; ... % 26
    -1, 24, 26; ... % 27
%
    29, 15, -1; ... % 28
    28, 16, 30; ... % 29
    -1, -1, 29; ... % 30
%
    32, 34, -1; ... % 31
    31, 35, 33; ... % 32
    -1, 10, 32; ... % 33
%
    35, 31, -1; ... % 34
    34, 32, 36; ... % 35
    -1, 13, 35 ];   % 36

  t1_ij = [ ...
    0, 0; ...
    2, 2; ...
    2, 0 ];

  return
end

