function value = hexahedron_unit_monomial_integral ( expon )

%*****************************************************************************80
%
%% hexahedron_unit_monomial_integral(): monomial integral in a unit hexahedron.
%
%  Discussion:
%
%    This routine returns the integral of
%
%      product ( 1 <= I <= 3 ) X(I)^EXPON(I)
%
%    over the unit hexahedron.
%
%    The unit hexahedron H is bounded by the vertices
%    (0,0,0), (1,0,0), (1,1,0), (0,1,0), (0,0,1), (1,0,1), (1,1,1), (0,1,1).
% 
%  Licensing:
%
%    This code is distributed under the MIT license.
%
%  Modified:
%
%    19 May 2023
%
%  Author:
%
%    John Burkardt
%
%  Input:
%
%    integer EXPON(3): the exponents.
%
%  Output:
%
%    real VALUE: the integral of the monomial.
%
  value = 1.0 / ( expon(1) + 1 ) ...
        * 1.0 / ( expon(2) + 1 ) ...
        * 1.0 / ( expon(3) + 1 );

  return
end
