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


/**
 * This class implements methods for generating random variates from the
 * Gumbel distribution. Its density is given by
 * 

 * 
 * 

 * f (x) = e-ze-e-z/| β|,        for  - ∞ < x < ∞.
 * 

 * where we use the notation 
 * z = (x - δ)/β. The scale parameter β
 * can be positive (for the Gumbel distribution) or negative (for the reverse
 * Gumbel distribution), but not 0.
 * 
 */
public class GumbelGen extends RandomVariateGen  {
   private double delta;
   private double beta;


   /**
    * Creates a Gumbel random number generator with
    *   β = 1 and 
    * δ = 0 using stream s.
    * 
    */
   public GumbelGen (RandomStream s)  {
      this (s, 1.0, 0.0);
   }


   /**
    * Creates a Gumbel random number generator with parameters
    * β = beta and δ = delta using stream s.
    * 
    */
   public GumbelGen (RandomStream s, double beta, double delta)  {
      super (s, new GumbelDist(beta, delta));
      setParams (beta, delta);
   }


   /**
    * Creates a new generator for the Gumbel distribution dist
    *    and stream s.
    * 
    */
   public GumbelGen (RandomStream s, GumbelDist dist)  {
      super (s, dist);
      if (dist != null)
         setParams (dist.getBeta(), dist.getDelta());
   } 


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


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


   /**
    * Returns the parameter δ.
    * 
    * 
    */
   public double getDelta() {
      return delta;
   }


   /**
    * Sets the parameters  β and δ of this object.
    * 
    */
   protected void setParams (double beta, double delta) {
     if (beta == 0.0)
         throw new IllegalArgumentException ("beta = 0");
      this.delta = delta;
      this.beta = beta;
   }

}