function [ n_data, x, fx ] = bessel_j1_values ( n_data )

%% BESSEL_J1_VALUES returns some values of the J1 Bessel function.
%
%  Discussion:
%
%    In Mathematica, the function can be evaluated by:
%
%      BesselJ[1,x]
%
%  Modified:
%
%    12 August 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 = [ ...
      0.3275791375914652E+00, ... 
      0.6604332802354914E-01, ... 
     -0.3390589585259365E+00, ... 
     -0.5767248077568734E+00, ... 
     -0.4400505857449335E+00, ... 
      0.0000000000000000E+00, ... 
      0.4400505857449335E+00, ... 
      0.5767248077568734E+00, ... 
      0.3390589585259365E+00, ... 
     -0.6604332802354914E-01, ... 
     -0.3275791375914652E+00, ... 
     -0.2766838581275656E+00, ... 
     -0.4682823482345833E-02, ... 
      0.2346363468539146E+00, ... 
      0.2453117865733253E+00, ... 
      0.4347274616886144E-01, ... 
     -0.1767852989567215E+00, ... 
     -0.2234471044906276E+00, ... 
     -0.7031805212177837E-01, ... 
      0.1333751546987933E+00, ... 
      0.2051040386135228E+00 ];

  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