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

%*****************************************************************************80
%
%% ARCTAN_INT_VALUES returns some values of the inverse tangent integral.
%
%  Discussion:
%
%    The function is defined by:
%
%      ARCTAN_INT(x) = Integral ( 0 <= t <= x ) arctan ( t ) / t dt
%
%    The data was reported by McLeod.
%
%  Licensing:
%
%    This code is distributed under the GNU LGPL license.
%
%  Modified:
%
%    15 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 = [ ...
      0.19531241721588483191E-02, ...
     -0.39062433772980711281E-02, ...
      0.78124470192576499535E-02, ...
      0.15624576181996527280E-01, ...
     -0.31246610349485401551E-01, ...
      0.62472911335014397321E-01, ...
      0.12478419717389654039E+00, ...
     -0.24830175098230686908E+00, ...
      0.48722235829452235711E+00, ...
      0.91596559417721901505E+00, ...
      0.12749694484943800618E+01, ...
     -0.15760154034463234224E+01, ...
      0.24258878412859089996E+01, ...
      0.33911633326292997361E+01, ...
      0.44176450919422186583E+01, ...
     -0.47556713749547247774E+01, ...
      0.50961912150934111303E+01, ...
      0.53759175735714876256E+01, ...
     -0.61649904785027487422E+01, ...
      0.72437843013083534973E+01 ];

  x_vec = [ ...
       0.0019531250E+00, ...
      -0.0039062500E+00, ...
       0.0078125000E+00, ...
       0.0156250000E+00, ...
      -0.0312500000E+00, ...
       0.0625000000E+00, ...
       0.1250000000E+00, ...
      -0.2500000000E+00, ...
       0.5000000000E+00, ...
       1.0000000000E+00, ...
       1.5000000000E+00, ...
      -2.0000000000E+00, ...
       4.0000000000E+00, ...
       8.0000000000E+00, ...
      16.0000000000E+00, ...
     -20.0000000000E+00, ...
      25.0000000000E+00, ...
      30.0000000000E+00, ...
     -50.0000000000E+00, ...
     100.0000000000E+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

  return
end
