function [ n_data, x, fx ] = debye4_values ( n_data )

%% DEBYE4_VALUES returns some values of Debye's function of order 4.
%
%  Discussion:
%
%    The function is defined by:
%
%      DEBYE4(x) = 4 / x^4 * Integral ( 0 <= t <= x ) t^4 / ( exp ( t ) - 1 ) dt
%
%    The data was reported by McLeod.
%
%  Modified:
%
%    16 September 2004
%
%  Author:
%
%    John Burkardt
%
%  Reference:
%
%    Allan McLeod,
%    Algorithm 757, MISCFUN: A software package to compute uncommon
%      special functions,
%    ACM Transactions on Mathematical Software,
%    Volume 22, Number 3, September 1996, pages 288-301.
%
%  Parameters:
%
%    Input/output, integer N_DATA.  The user sets N_DATA to 0 before the
%    first call.  On each call, the routine increments N_DATA by 1, and
%    returns the corresponding data; when there is no more data, the
%    output value of N_DATA will be 0 again.
%
%    Output, real X, the argument of the function.
%
%    Output, real FX, the value of the function.
%
  n_max = 20;

  fx_vec = [ ...
      0.99921896192761576256E+00, ...
      0.98755425280996071022E+00, ...
      0.95086788606389739976E+00, ...
      0.81384569172034042516E+00, ...
      0.65487406888673697092E+00, ...
      0.52162830964878715188E+00, ...
      0.41189273671788528876E+00, ...
      0.32295434858707304628E+00, ...
      0.25187863642883314410E+00, ...
      0.15185461258672022043E+00, ...
      0.13372661145921413299E+00, ...
      0.91471377664481164749E-01, ...
      0.71227828197462523663E-01, ...
      0.55676547822738862783E-01, ...
      0.21967566525574960096E-01, ...
      0.96736755602711590082E-02, ...
      0.19646978158351837850E-02, ...
      0.62214648623965450200E-03, ...
      0.12289514092077854510E-03, ...
      0.15927210319002161231E-04 ];

  x_vec = [ ...
       0.0019531250E+00, ...
       0.0312500000E+00, ...
       0.1250000000E+00, ...
       0.5000000000E+00, ...
       1.0000000000E+00, ...
       1.5000000000E+00, ...
       2.0000000000E+00, ...
       2.5000000000E+00, ...
       3.0000000000E+00, ...
       4.0000000000E+00, ...
       4.2500000000E+00, ...
       5.0000000000E+00, ...
       5.5000000000E+00, ...
       6.0000000000E+00, ...
       8.0000000000E+00, ...
      10.0000000000E+00, ...
      15.0000000000E+00, ...
      20.0000000000E+00, ...
      30.0000000000E+00, ...
      50.0000000000E+00 ];       

  if ( n_data < 0 )
    n_data = 0;
  end

  n_data = n_data + 1;

  if ( n_max < n_data )
    n_data = 0;
    x = 0.0;
    fx = 0.0;
  else
    x = x_vec(n_data);
    fx = fx_vec(n_data);
  end