package umontreal.iro.lecuyer.randvar;
import umontreal.iro.lecuyer.rng.*;
import umontreal.iro.lecuyer.probdist.*;


/**
 * This class implements random variate generators for the
 * Rayleigh distribution.
 *  Its density is
 * 

 * 

 * 
 * 
 * 
 * 
 * 
 * 
 * 
 * 
 * 
 * 
 * 
f (x)
=
(x-a) e-(x-a)2/(2β2)/β2        for x >= a

 *  
f (x)
=
0        for x < a,

 *  
 * 

 * 
 * where β > 0.
 * 
 */
public class RayleighGen extends RandomVariateGen  {
   private double a;
   private double beta;


   /**
    * Creates a Rayleigh random variate generator with parameters
    *  a = a and β = beta, using stream s.
    * 
    */
   public RayleighGen (RandomStream s, double a, double beta)  {
      super (s, new RayleighDist(a, beta));
      setParams (a, beta);
   }


   /**
    * Creates a Rayleigh random variate generator with parameters
    *  a = 0 and β = beta, using stream s.
    * 
    */
   public RayleighGen (RandomStream s, double beta)  {
      this (s, 0.0, beta);
   }


   /**
    * Creates a new generator for the Rayleigh distribution dist
    *    and stream s.
    * 
    */
   public RayleighGen (RandomStream s, RayleighDist dist)  {
      super (s, dist);
      if (dist != null)
         setParams (dist.getA(), dist.getSigma());
   } 


   /**
    * Uses inversion to generate a new variate from the Rayleigh
    *    distribution with parameters a = a and
    *    β = beta, using stream s.
    * 
    */
   public static double nextDouble (RandomStream s, double a, double beta)  {
       return RayleighDist.inverseF (a, beta, s.nextDouble());
   }


   /**
    * Returns the parameter a.
    * 
    */
   public double getA() {
      return a;
   }


   /**
    * Returns the parameter β.
    * 
    */
   public double getSigma() {
      return beta;
   }


   /**
    * Sets the parameters a = a and β = beta
    *  for this object.
    * 
    */
   public void setParams (double a, double beta)  {
      if (beta <= 0.0)
         throw new IllegalArgumentException ("beta <= 0");
      this.a  = a;
      this.beta = beta;
   }

}