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


/**
 * This class implements random variate generators for the 
 * exponential distribution. The density is
 * 
 * 

 * 

 * f (x) = λe-λx         for x >= 0,
 * 

 * where 
 * λ > 0.
 * 
 * 

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



   /**
    * Creates an exponential random variate generator with
    *  parameter λ = lambda, using stream s.
    * 
    */
   public ExponentialGen (RandomStream s, double lambda)  {
      super (s, new ExponentialDist(lambda));
      setParams (lambda);
   }


   /**
    * Creates a new generator for the exponential 
    *    distribution dist and stream s.
    * 
    */
   public ExponentialGen (RandomStream s, ExponentialDist dist)  {
      super (s, dist);
      if (dist != null)
         setParams (dist.getLambda());
   } 

   
   /**
    * Uses inversion to generate a new exponential variate
    *    with parameter λ = lambda, using stream s.
    * 
    */
   public static double nextDouble (RandomStream s, double lambda)  {
      return ExponentialDist.inverseF (lambda, s.nextDouble());
   }


   /**
    * Returns the λ associated with this object.
    * 
    * 
    */
   public double getLambda() {
      return lambda;
   }



   /**
    * Sets the parameter λ = lam of this object.
    * 
    */
   protected void setParams (double lam) {
      if (lam <= 0.0)
         throw new IllegalArgumentException ("lambda <= 0");
      this.lambda = lam;
   }

}