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

# include "asa063.h"

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

double betain ( double x, double p, double q, double beta, int *ifault )

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

    betain() computes the incomplete Beta function ratio.

  Licensing:

    This code is distributed under the MIT license. 

  Modified:

    31 October 2010

  Author:

    Original FORTRAN77 version by KL Majumder, GP Bhattacharjee.
    This version by John Burkardt.

  Reference:

    KL Majumder, GP Bhattacharjee,
    Algorithm AS 63:
    The incomplete Beta Integral,
    Applied Statistics,
    Volume 22, Number 3, 1973, pages 409-411.

  Input:

    double X, the argument, between 0 and 1.

    double P, Q, the parameters, which
    must be positive.

    double BETA, the logarithm of the complete
    beta function.

  Output:

    int *IFAULT, error flag.
    0, no error.
    nonzero, an error occurred.

    double BETAIN, the value of the incomplete
    Beta function ratio.
*/
{
  double acu = 0.1E-14;
  double ai;
  double cx;
  int indx;
  int ns;
  double pp;
  double psq;
  double qq;
  double rx;
  double temp;
  double term;
  double value;
  double xx;

  value = x;
  *ifault = 0;
/*
  Check the input arguments.
*/
  if ( p <= 0.0 || q <= 0.0 )
  {
    *ifault = 1;
    return value;
  }

  if ( x < 0.0 || 1.0 < x )
  {
    *ifault = 2;
    return value;
  }
/*
  Special cases.
*/
  if ( x == 0.0 || x == 1.0 )
  {
    return value;
  }
/*
  Change tail if necessary and determine S.
*/
  psq = p + q;
  cx = 1.0 - x;

  if ( p < psq * x )
  {
    xx = cx;
    cx = x;
    pp = q;
    qq = p;
    indx = 1;
  }
  else
  {
    xx = x;
    pp = p;
    qq = q;
    indx = 0;
  }

  term = 1.0;
  ai = 1.0;
  value = 1.0;
  ns = ( int ) ( qq + cx * psq );
/*
  Use the Soper reduction formula.
*/
  rx = xx / cx;
  temp = qq - ai;
  if ( ns == 0 )
  {
    rx = xx;
  }

  for ( ; ; )
  {
    term = term * temp * rx / ( pp + ai );
    value = value + term;;
    temp = fabs ( term );

    if ( temp <= acu && temp <= acu * value )
    {
      value = value * exp ( pp * log ( xx ) 
      + ( qq - 1.0 ) * log ( cx ) - beta ) / pp;

      if ( indx )
      {
        value = 1.0 - value;
      }
      break;
    }

    ai = ai + 1.0;
    ns = ns - 1;

    if ( 0 <= ns )
    {
      temp = qq - ai;
      if ( ns == 0 )
      {
        rx = xx;
      }
    }
    else
    {
      temp = psq;
      psq = psq + 1.0;
    }
  }

  return value;
}
/******************************************************************************/

void beta_inc_values ( int *n_data, double *a, double *b, double *x,
  double *fx )

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

    beta_inc_values() returns some values of the incomplete Beta function.

  Discussion:

    The incomplete Beta function may be written

      BETA_INC(A,B,X) = Integral (0 <= T <= X) T^(A-1) * (1-T)^(B-1) dT
                      / Integral (0 <= T <= 1) T^(A-1) * (1-T)^(B-1) dT

    Thus,

      BETA_INC(A,B,0.0) = 0.0;
      BETA_INC(A,B,1.0) = 1.0

    The incomplete Beta function is also sometimes called the
    "modified" Beta function, or the "normalized" Beta function
    or the Beta CDF (cumulative density function.

    In Mathematica, the function can be evaluated by:

      BETA[X,A,B] / BETA[A,B]

    The function can also be evaluated by using the Statistics package:

      Needs["Statistics`ContinuousDistributions`"]
      dist = BetaDistribution [ a, b ]
      CDF [ dist, x ]

  Licensing:

    This code is distributed under the MIT license.

  Modified:

    28 April 2013

  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.

    Karl Pearson,
    Tables of the Incomplete Beta Function,
    Cambridge University Press, 1968.

    Stephen Wolfram,
    The Mathematica Book,
    Fourth Edition,
    Cambridge University Press, 1999,
    ISBN: 0-521-64314-7,
    LC: QA76.95.W65.

  Input:

    int *N_DATA.  The user sets N_DATA to 0 before the
    first call.  

  Output:

    int *N_DATA: 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.

    double *A, B, the parameters of the function.

    double *X, the argument of the function.

    double *FX, the value of the function.
*/
{
# define N_MAX 45

  static double a_vec[N_MAX] = {
      0.5E+00,
      0.5E+00,
      0.5E+00,
      1.0E+00,
      1.0E+00,
      1.0E+00,
      1.0E+00,
      1.0E+00,
      2.0E+00,
      2.0E+00,
      2.0E+00,
      2.0E+00,
      2.0E+00,
      2.0E+00,
      2.0E+00,
      2.0E+00,
      2.0E+00,
      5.5E+00,
     10.0E+00,
     10.0E+00,
     10.0E+00,
     10.0E+00,
     20.0E+00,
     20.0E+00,
     20.0E+00,
     20.0E+00,
     20.0E+00,
     30.0E+00,
     30.0E+00,
     40.0E+00,
      0.1E+01,
      0.1E+01,
      0.1E+01,
      0.1E+01,
      0.1E+01,
      0.1E+01,
      0.1E+01,
      0.1E+01,
      0.2E+01,
      0.3E+01,
      0.4E+01,
      0.5E+01,
      1.30625, 
      1.30625, 
      1.30625 };

  static double b_vec[N_MAX] = {
      0.5E+00,
      0.5E+00,
      0.5E+00,
      0.5E+00,
      0.5E+00,
      0.5E+00,
      0.5E+00,
      1.0E+00,
      2.0E+00,
      2.0E+00,
      2.0E+00,
      2.0E+00,
      2.0E+00,
      2.0E+00,
      2.0E+00,
      2.0E+00,
      2.0E+00,
      5.0E+00,
      0.5E+00,
      5.0E+00,
      5.0E+00,
     10.0E+00,
      5.0E+00,
     10.0E+00,
     10.0E+00,
     20.0E+00,
     20.0E+00,
     10.0E+00,
     10.0E+00,
     20.0E+00,
      0.5E+00,
      0.5E+00,
      0.5E+00,
      0.5E+00,
      0.2E+01,
      0.3E+01,
      0.4E+01,
      0.5E+01,
      0.2E+01,
      0.2E+01,
      0.2E+01,
      0.2E+01,
     11.7562,
     11.7562, 
     11.7562 };

  static double fx_vec[N_MAX] = {
     0.6376856085851985E-01,
     0.2048327646991335E+00,
     0.1000000000000000E+01,
     0.0000000000000000E+00,
     0.5012562893380045E-02,
     0.5131670194948620E-01,
     0.2928932188134525E+00,
     0.5000000000000000E+00,
     0.2800000000000000E-01,
     0.1040000000000000E+00,
     0.2160000000000000E+00,
     0.3520000000000000E+00,
     0.5000000000000000E+00,
     0.6480000000000000E+00,
     0.7840000000000000E+00,
     0.8960000000000000E+00,
     0.9720000000000000E+00,
     0.4361908850559777E+00,
     0.1516409096347099E+00,
     0.8978271484375000E-01,
     0.1000000000000000E+01,
     0.5000000000000000E+00,
     0.4598773297575791E+00,
     0.2146816102371739E+00,
     0.9507364826957875E+00,
     0.5000000000000000E+00,
     0.8979413687105918E+00,
     0.2241297491808366E+00,
     0.7586405487192086E+00,
     0.7001783247477069E+00,
     0.5131670194948620E-01,
     0.1055728090000841E+00,
     0.1633399734659245E+00,
     0.2254033307585166E+00,
     0.3600000000000000E+00,
     0.4880000000000000E+00,
     0.5904000000000000E+00,
     0.6723200000000000E+00,
     0.2160000000000000E+00,
     0.8370000000000000E-01,
     0.3078000000000000E-01,
     0.1093500000000000E-01,
     0.918884684620518,
     0.21052977489419,
     0.1824130512500673 };

  static double x_vec[N_MAX] = {
     0.01E+00,
     0.10E+00,
     1.00E+00,
     0.00E+00,
     0.01E+00,
     0.10E+00,
     0.50E+00,
     0.50E+00,
     0.10E+00,
     0.20E+00,
     0.30E+00,
     0.40E+00,
     0.50E+00,
     0.60E+00,
     0.70E+00,
     0.80E+00,
     0.90E+00,
     0.50E+00,
     0.90E+00,
     0.50E+00,
     1.00E+00,
     0.50E+00,
     0.80E+00,
     0.60E+00,
     0.80E+00,
     0.50E+00,
     0.60E+00,
     0.70E+00,
     0.80E+00,
     0.70E+00,
     0.10E+00,
     0.20E+00,
     0.30E+00,
     0.40E+00,
     0.20E+00,
     0.20E+00,
     0.20E+00,
     0.20E+00,
     0.30E+00,
     0.30E+00,
     0.30E+00,
     0.30E+00,
     0.225609, 
     0.0335568, 
     0.0295222 };

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

  *n_data = *n_data + 1;

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

  return;
# undef N_MAX
}