function dot = lo_dot ( L1, L2 )

%*****************************************************************************80
%
%% lo_dot() computes the dot product modulo 2 of two configurations.
%
%  Discussion:
%
%    A given 5x5 Lights Out configuration L is solvable if and only if
%    if is orthogonal to both the N1 and N2 solvability matrices.
%
%    Here orthogonal means orthogonal modulo 2.  You take the element-wise
%    dot product of the two matrices modulo 2.  If it is zero, then they
%    are orthogonal.
%
%  Licensing:
%
%    This code is distributed under the MIT license.
%
%  Modified:
%
%    11 November 2024
%
%  Author:
%
%    John Burkardt
%
%  Input:
%
%    logical L1(5,5), L2(5,5): the configurations to check.
%
%  Output:
%
%    integer dot: 0 or 1.
%
  dot = mod ( sum ( sum ( L1 .* L2 ) ), 2 );

  return
end

