/***************************************************************************
 * Copyright (C) 1995, 1996, Jun Sun, jsun@junsun.net.                     *
 *                                                                         *
 ***************************************************************************
 */
/* implementation of exponential distribution */
/* only random generator are implemented currently */
#include <math.h>
#include <assert.h>
#include "random_variates.h"

Exponential::Exponential(double beta)
{
  _beta = beta;
}

Exponential::~Exponential(){}

double Exponential::sample()
{ 
  return -_beta * log(randp->sample());
}

double Exponential::distribution(double x)
{ 
  if (x<0.0)
    return 0.0;
  else
    return 1.0 - exp(-x/_beta);
}
 
double Exponential::density(double x)
{
  if (x<0.0)
    return 0.0;
  else
    return exp(-x/_beta)/_beta;
}

double Exponential::probability(double x1, double x2)
{
 assert(x2>=x1);

 return distribution(x2) - distribution(x1);
}

double Exponential::inverse_distribution(double p)
{
  return -_beta * log(1-p);
}