package umontreal.iro.lecuyer.randvar;

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


/**
 * This class implements random variate generators for 
 * the Pearson type VI distribution with shape parameters
 * 
 * α1 > 0 and 
 * α2 > 0, and scale parameter β > 0.
 * The density function of this distribution is
 * 
 * 

 * 

 * f (x) = (x/β)α1-1/(βB(α1, α2)[1 + x/β]α1+α2)        for x > 0,
 * 

 * and f (x) = 0 otherwise,
 * where B is the beta function.
 * 
 */
public class Pearson6Gen extends RandomVariateGen  {
   protected double alpha1;
   protected double alpha2;
   protected double beta;




   /**
    * Creates a Pearson6 random variate generator with parameters
    *   α1 = alpha1, α2 = alpha2 and β =
    *   beta, using stream s.
    * 
    */
   public Pearson6Gen (RandomStream s, double alpha1, double alpha2,
                                       double beta)  {
      super (s, new Pearson6Dist(alpha1, alpha2, beta));
      setParams (alpha1, alpha2, beta);
   }


   /**
    * Creates a Pearson6 random variate generator with parameters
    *   
    * α1 = alpha1, α2 = alpha2 and β = 1,
    *     using stream s.
    * 
    */
   public Pearson6Gen (RandomStream s, double alpha1, double alpha2)  {
      this (s, alpha1, alpha2, 1.0);
   }


   /**
    * Creates a new generator for the distribution dist,
    *      using stream s.
    * 
    */
   public Pearson6Gen (RandomStream s, Pearson6Dist dist)  {
      super (s, dist);
      if (dist != null)
         setParams(dist.getAlpha1(), dist.getAlpha2(), dist.getBeta());
   }


   /**
    * Generates a variate from the Pearson VI distribution
    *    with shape parameters 
    * α1 > 0 and 
    * α2 > 0, and
    *    scale parameter β > 0.
    * 
    */
   public static double nextDouble (RandomStream s, double alpha1,
                                    double alpha2, double beta) {
      return Pearson6Dist.inverseF (alpha1, alpha2, beta, s.nextDouble());
   }


   /**
    * Returns the α1 parameter of this object.
    * 
    */
   public double getAlpha1() {
      return alpha1;
   }


   /**
    * Returns the α2 parameter of this object.
    * 
    */
   public double getAlpha2() {
      return alpha2;
   }


   /**
    * Returns the β parameter of this object.
    * 
    * 
    */
   public double getBeta() {
      return beta;
   }

   
   /**
    * Sets the parameters α1, α2 and β of this object.
    * 
    */
   public void setParams (double alpha1, double alpha2, double beta) {
      if (alpha1 <= 0.0)
         throw new IllegalArgumentException("alpha1 <= 0");
      if (alpha2 <= 0.0)
         throw new IllegalArgumentException("alpha2 <= 0");
      if (beta <= 0.0)
         throw new IllegalArgumentException("beta <= 0");
      this.alpha1 = alpha1;
      this.alpha2 = alpha2;
      this.beta = beta;
   }

}