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


/**
 * This class implements random variate generators for one of the Pareto
 * distributions, with parameters α > 0 and β > 0.
 * Its density function is
 * 

 * 
 * 

 * f (x) = αβα / xα+1 for x > β, 0 otherwise.
 * 

 * The (non-static) nextDouble method simply calls inverseF on the
 * distribution.
 * 
 */
public class ParetoGen extends RandomVariateGen  {
   protected double alpha;
   protected double beta;


   /**
    * Creates a Pareto random variate generator with parameters α = 
    *    alpha and β = beta, using stream s.
    * 
    */
   public ParetoGen (RandomStream s, double alpha, double beta)  {
      super (s, new ParetoDist(alpha, beta));
      setParams(alpha, beta);
   }


   /**
    * Creates a Pareto random variate generator with parameters α = 
    *    alpha and β = 1, using stream s.
    * 
    */
   public ParetoGen (RandomStream s, double alpha)  {
      this (s, alpha, 1.0);
   }


   /**
    * Creates a new generator for the Pareto distribution
    *    dist and stream s.
    * 
    */
   public ParetoGen (RandomStream s, ParetoDist dist)  {
      super (s, dist);
      if (dist != null)
         setParams(dist.getAlpha(), dist.getBeta());
   }


   /**
    * Generates a new variate from the Pareto distribution
    *    with parameters α = alpha and β = beta, 
    *    using stream s.
    * 
    */
   public static double nextDouble (RandomStream s,
                                    double alpha, double beta) {
      return ParetoDist.inverseF (alpha, beta, s.nextDouble());
   }


   /**
    * Returns the parameter α of this object.
    * 
    */
   public double getAlpha() {
      return alpha;
   }


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


   protected void setParams (double alpha, double beta) {
      if (alpha <= 0.0)
         throw new IllegalArgumentException ("alpha <= 0");
      if (beta <= 0.0)
         throw new IllegalArgumentException ("beta <= 0");
      this.alpha = alpha;
      this.beta = beta;
   }
}