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

%*****************************************************************************80
%
%% ERFC_VALUES returns some values of the ERFC or "complementary error" function.
%
%  Discussion:
%
%    The complementary error function is defined by:
%
%      ERFC(X) = 1 - ( 2 / sqrt ( PI ) * integral ( 0 <= T <= X ) exp ( - T^2 ) dT
%
%    In Mathematica, the function can be evaluated by:
%
%      Erfc[x]
%
%  Licensing:
%
%    This code is distributed under the GNU LGPL license.
%
%  Modified:
%
%    20 May 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.
%
%  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 = 21;

  fx_vec = [ ...
    1.000000000000000E+00, ...
    0.7772974107895215E+00, ...
    0.5716076449533315E+00, ...
    0.3961439091520741E+00, ...
    0.2578990352923395E+00, ...
    0.1572992070502851E+00, ...
    0.08968602177036462E+00, ...
    0.04771488023735119E+00, ...
    0.02365161665535599E+00, ...
    0.01090949836426929E+00, ...
    0.004677734981047266E+00, ...
    0.001862846297981891E+00, ...
    0.0006885138966450786E+00, ...
    0.0002360344165293492E+00, ...
    0.00007501319466545902E+00, ...
    0.00002209049699858544E+00, ...
    6.025761151762095E-06, ...
    1.521993362862285E-06, ...
    3.558629930076853E-07, ...
    7.700392745696413E-08, ...
    1.541725790028002E-08  ]; 

  x_vec = [ ...
    0.0E+00, ... 
    0.2E+00, ... 
    0.4E+00, ... 
    0.6E+00, ... 
    0.8E+00, ... 
    1.0E+00, ... 
    1.2E+00, ... 
    1.4E+00, ... 
    1.6E+00, ... 
    1.8E+00, ... 
    2.0E+00, ...
    2.2E+00, ... 
    2.4E+00, ... 
    2.6E+00, ... 
    2.8E+00, ... 
    3.0E+00, ... 
    3.2E+00, ... 
    3.4E+00, ... 
    3.6E+00, ... 
    3.8E+00, ... 
    4.0E+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
