function value = mono_between_enum ( d, n1, n2 )

%*****************************************************************************80
%
%% MONO_BETWEEN_ENUM enumerates monomials in D dimensions of degrees in a range.
%
%  Discussion:
%
%    For D = 3, we have the following table:
%
%     N2 0  1  2  3  4  5  6   7   8
%   N1 +----------------------------
%    0 | 1  4 10 20 35 56 84 120 165
%    1 | 0  3  9 19 34 55 83 119 164
%    2 | 0  0  6 16 31 52 80 116 161
%    3 | 0  0  0 10 25 46 74 110 155
%    4 | 0  0  0  0 15 36 64 100 145
%    5 | 0  0  0  0  0 21 49  85 130
%
%  Licensing:
%
%    This code is distributed under the GNU LGPL license.
%
%  Modified:
%
%    18 November 2013
%
%  Author:
%
%    John Burkardt
%
%  Parameters:
%
%    Input, integer D, the spatial dimension.
%
%    Input, integer N1, N2, the minimum and maximum degrees.
%    0 <= N1 <= N2.
%
%    Output, integer VALUE, the number of monomials in D variables,
%    of total degree between N1 and N2 inclusive.
%
  n1 = max ( n1, 0 );

  if ( n2 < n1 )
    value = 0;
    return
  end

  if ( n1 == 0 )
    value = nchoosek ( n2 + d, n2 );
  else if ( n1 == n2 )
    value = nchoosek ( n2 + d - 1, n2 );
  else
    n0 = n1 - 1;
    value = nchoosek ( n2 + d, n2 ) - nchoosek ( n0 + d, n0 );
  end

  return
end

