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

%*****************************************************************************80
%
%% chi_values() returns some values of the hyperbolic cosine integral function.
%
%  Discussion:
%
%      CHI(X) = gamma + log ( x ) 
%        + integral ( 0 <= T < X ) ( cosh ( T ) - 1 ) / T  dT
%
%    where gamma is Euler's constant.
%
%    In Mathematica, the function can be evaluated by:
%
%      CoshIntegral[x]
%
%  Licensing:
%
%    This code is distributed under the MIT license.
%
%  Modified:
%
%    11 June 2007
%
%  Author:
%
%    John Burkardt
%
%  Reference:
%
%    Milton Abramowitz, Irene Stegun,
%    Handbook of Mathematical Functions,
%    National Bureau of Standards, 1964,
%    ISBN: 0-486-61272-4,
%    LC: QA47.A34.
%
%    Stephen Wolfram,
%    The Mathematica Book,
%    Fourth Edition,
%    Cambridge University Press, 1999,
%    ISBN: 0-521-64314-7,
%    LC: QA76.95.W65.
%
%  Input:
%
%    integer N_DATA.  The user sets N_DATA to 0 before the first call.  
%    Thereafter, it should simply be the value returned by the previous call.
%
%  Output:
%
%    integer N_DATA.  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.
%
%    real X, the argument of the function.
%
%    real FX, the value of the function.
%
  n_max = 16;

  fx_vec = [ ...
    -0.05277684495649362, ...
     0.1577508933739787, ...
     0.3455691756953907, ...
     0.5183999848333915, ...
     0.6813138871854339, ...
     0.8378669409802082, ...
     1.141841924170595, ...
     1.445494075789644, ...
     1.759505807660965, ...
     2.092577214062032, ...
     2.452666922646915, ...
     3.524425488354165, ...
     4.960392094765610, ...
     6.959191927647393, ...
     9.813547558823186, ...
    13.96581164859243 ];

  x_vec = [ ...
      0.5E+00, ...
      0.6E+00, ...
      0.7E+00, ...
      0.8E+00, ...
      0.9E+00, ...
      1.0E+00, ...
      1.2E+00, ...
      1.4E+00, ...
      1.6E+00, ...
      1.8E+00, ...
      2.0E+00, ...
      2.5E+00, ...
      3.0E+00, ...
      3.5E+00, ...
      4.0E+00, ...
      4.5E+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

