/***************************************************************************
 * Copyright (C) 1995, 1996, Jun Sun, jsun@junsun.net.                     *
 *                                                                         *
 ***************************************************************************
 */
/* implementation of negtive geometric distribution */

#include <math.h>
#include "macro.h"
#include "random_variates.h"

Geometric::Geometric(double p)
{
  _p = p;
}

Geometric::Geometric(int *data, int num_data)
{
  double sum = 0.0;
  for(int i=0;i<num_data;i++)
    sum += data[i];

  _p = 1.0 / (1.0 + sum / (double) num_data);
}

Geometric::~Geometric() {}


double Geometric::mass(int x)
{ if (x<0)
    return 0.0;
  else
    return _p*pow(1-_p,(double)x);
}


double Geometric::distribution(double x)
{
  if (x<0.0) return 0;

  return 1.0 - pow(1-_p,(double)FLOOR(x)+1.0);
}

int Geometric::sample()
{ double temp = randp->sample();
  return FLOOR(log(temp) / (log(1.0 - _p)));
}