function [ n_data, x, fx ] = bessel_j0_values ( n_data )

%*****************************************************************************80
%
%% BESSEL_J0_VALUES returns some values of the J0 Bessel function.
%
%  Discussion:
%
%    In Mathematica, the function can be evaluated by:
%
%      BesselJ[0,x]
%
%  Licensing:
%
%    This code is distributed under the GNU LGPL license.
%
%  Modified:
%
%    15 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 = 21;

  fx_vec = [ ...
     -0.1775967713143383E+00, ...
     -0.3971498098638474E+00, ...
     -0.2600519549019334E+00, ...
      0.2238907791412357E+00, ...
      0.7651976865579666E+00, ...
      0.1000000000000000E+01, ...
      0.7651976865579666E+00, ...
      0.2238907791412357E+00, ...
     -0.2600519549019334E+00, ...
     -0.3971498098638474E+00, ...
     -0.1775967713143383E+00, ...
      0.1506452572509969E+00, ...
      0.3000792705195556E+00, ...
      0.1716508071375539E+00, ...
     -0.9033361118287613E-01, ...
     -0.2459357644513483E+00, ...
     -0.1711903004071961E+00, ...
      0.4768931079683354E-01, ...
      0.2069261023770678E+00, ...
      0.1710734761104587E+00, ...
     -0.1422447282678077E-01 ];

  x_vec = [ ...
     -5.0E+00, ...
     -4.0E+00, ...
     -3.0E+00, ...
     -2.0E+00, ...
     -1.0E+00, ...
      0.0E+00, ...
      1.0E+00, ...
      2.0E+00, ...
      3.0E+00, ...
      4.0E+00, ...
      5.0E+00, ...
      6.0E+00, ...
      7.0E+00, ...
      8.0E+00, ...
      9.0E+00, ...
     10.0E+00, ...
     11.0E+00, ...
     12.0E+00, ...
     13.0E+00, ...
     14.0E+00, ...
     15.0E+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

