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

%*****************************************************************************80
%
%% TRIGAMMA_VALUES returns some values of the TriGamma function.
%
%  Discussion:
%
%    In Mathematica, the function can be evaluated by:
%
%      PolyGamma[1,x]
%
%    TriGamma(X) = d^2 ln ( Gamma ( X ) ) / d X^2
%
%  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.
%
%    Stephen Wolfram,
%    The Mathematica Book,
%    Fourth Edition,
%    Wolfram Media / Cambridge University Press, 1999.
%
%  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 = 11;

  fx_vec = [ ...
     0.1644934066848226E+01, ...
     0.1433299150792759E+01, ...
     0.1267377205423779E+01, ...
     0.1134253434996619E+01, ...
     0.1025356590529597E+01, ...
     0.9348022005446793E+00, ...
     0.8584318931245799E+00, ...
     0.7932328301639984E+00, ...
     0.7369741375017002E+00, ...
     0.6879720582426356E+00, ...
     0.6449340668482264E+00 ];

  x_vec = [ ...
    1.0E+00, ...
    1.1E+00, ...
    1.2E+00, ...
    1.3E+00, ...
    1.4E+00, ...
    1.5E+00, ...
    1.6E+00, ...
    1.7E+00, ...
    1.8E+00, ...
    1.9E+00, ...
    2.0E+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
