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

%*****************************************************************************80
%
%% CLAUSEN_VALUES returns some values of the Clausen's integral.
%
%  Discussion:
%
%    The function is defined by:
%
%      CLAUSEN(x) = Integral ( 0 <= t <= x ) -ln ( 2 * sin ( t / 2 ) ) dt
%
%    The data was reported by McLeod.
%
%  Licensing:
%
%    This code is distributed under the GNU LGPL license.
%
%  Modified:
%
%    16 September 2004
%
%  Author:
%
%    John Burkardt
%
%  Reference:
%
%    Milton Abramowitz and Irene Stegun,
%    Handbook of Mathematical Functions,
%    US Department of Commerce, 1964, page 1006.
%
%    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 = [ ...
      0.14137352886760576684E-01, ...
      0.13955467081981281934E+00, ...
     -0.38495732156574238507E+00, ...
      0.84831187770367927099E+00, ...
      0.10139591323607685043E+01, ...
     -0.93921859275409211003E+00, ...
      0.72714605086327924743E+00, ...
      0.43359820323553277936E+00, ...
     -0.98026209391301421161E-01, ...
     -0.56814394442986978080E+00, ...
     -0.70969701784448921625E+00, ...
      0.99282013254695671871E+00, ...
     -0.98127747477447367875E+00, ...
     -0.64078266570172320959E+00, ...
      0.86027963733231192456E+00, ...
      0.39071647608680211043E+00, ...
      0.47574793926539191502E+00, ...
      0.10105014481412878253E+01, ...
      0.96332089044363075154E+00, ...
     -0.61782699481929311757E+00 ];

  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

  return
end
