# include <math.h>
# include <stdio.h>
# include <stdlib.h>

# include "asa091.h"

/******************************************************************************/

void chi_square_cdf_values ( int *n_data, int *a, double *x, double *fx )

/******************************************************************************/
/*
  Purpose:

    chi_square_cdf_values() returns some values of the Chi-Square CDF.

  Discussion:

    In Mathematica, the function can be evaluated by:

      Needs["Statistics`ContinuousDistributions`"]
      dist = ChiSquareDistribution [ df ]
      CDF [ dist, x ]

  Licensing:

    This code is distributed under the MIT license. 

  Modified:

    09 August 2004

  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, int *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, int *A, the parameter of the function.

    Output, double *X, the argument of the function.

    Output, double *FX, the value of the function.
*/
{
# define N_MAX 21

  int a_vec[N_MAX] = { 
     1,  2,  1,  2, 
     1,  2,  3,  4, 
     1,  2,  3,  4, 
     5,  3,  3,  3, 
     3,  3, 10, 10, 
    10 };

  double fx_vec[N_MAX] = { 
     0.7965567455405796E-01,  
     0.4987520807317687E-02,   
     0.1124629160182849E+00,  
     0.9950166250831946E-02,  
     0.4729107431344619E+00,   
     0.1812692469220181E+00,   
     0.5975750516063926E-01,   
     0.1752309630642177E-01,   
     0.6826894921370859E+00,   
     0.3934693402873666E+00,   
     0.1987480430987992E+00,   
     0.9020401043104986E-01,   
     0.3743422675270363E-01,   
     0.4275932955291202E+00,   
     0.6083748237289110E+00,   
     0.7385358700508894E+00,   
     0.8282028557032669E+00,   
     0.8883897749052874E+00,   
     0.1721156299558408E-03,   
     0.3659846827343712E-02,   
     0.1857593622214067E-01 };

  double x_vec[N_MAX] = { 
     0.01E+00,   
     0.01E+00,    
     0.02E+00,   
     0.02E+00,   
     0.40E+00,   
     0.40E+00,   
     0.40E+00,   
     0.40E+00,   
     1.00E+00,   
     1.00E+00,   
     1.00E+00,   
     1.00E+00,   
     1.00E+00,   
     2.00E+00,   
     3.00E+00,   
     4.00E+00,   
     5.00E+00,   
     6.00E+00,   
     1.00E+00,   
     2.00E+00,   
     3.00E+00 };

  if ( *n_data < 0 )
  {
    *n_data = 0;
  }

  *n_data = *n_data + 1;

  if ( N_MAX < *n_data )
  {
    *n_data = 0;
    *a = 0;
    *x = 0.0;
    *fx = 0.0;
  }
  else
  {
    *a = a_vec[*n_data-1];
    *x = x_vec[*n_data-1];
    *fx = fx_vec[*n_data-1];
  }

  return;
# undef N_MAX
}