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 
 * lognormal distribution. Its density is
 * 
 * 

 * 

 * f (x) = (1/((2π)1/2σx)e-(ln(x)-μ)2/(2σ2) for x > 0,
 * 

 * where σ > 0.
 * 
 * 

 * The (non-static) nextDouble method simply calls inverseF on the
 * lognormal distribution object.
 * One can also generate a lognormal random variate X via 
 * 
 * 

 * 

 * X = Math.exp (NormalGen.nextDouble (s, mu, sigma)),
 * 

 * in which
 * NormalGen can actually be replaced by any subclass of NormalGen.
 * 
 */
public class LognormalGen extends RandomVariateGen  {
   private double mu;
   private double sigma = -1.0;



   /**
    * Creates a lognormal random variate generator with parameters
    *    μ = mu and σ = sigma, using stream s.
    * 
    */
   public LognormalGen (RandomStream s, double mu, double sigma)  {
      this (s, new LognormalDist(mu, sigma));
      setParams (mu, sigma);
   }


   /**
    * Creates a lognormal random variate generator with parameters
    *  μ = 0 and  
    * σ = 1, using stream s.
    * 
    */
   public LognormalGen (RandomStream s)  {
      this (s, 0.0, 1.0);
   }


   /**
    * Create a random variate generator for the lognormal 
    *    distribution dist and stream s.
    * 
    */
   public LognormalGen (RandomStream s, LognormalDist dist)  {
      super (s, dist);
      if (dist != null)
         setParams (dist.getMu(), dist.getSigma());
   }


   /**
    * Generates a new variate from the lognormal
    *     distribution with parameters μ = mu and
    *     σ = sigma, using stream s.
    * 
    */
   public static double nextDouble (RandomStream s, double mu, double sigma) {
      return LognormalDist.inverseF (mu, sigma, s.nextDouble());
   }
      

   /**
    * Returns the parameter μ of this object.
    * 
    */
   public double getMu() {
      return mu;
   }


   /**
    * Returns the parameter σ of this object.
    * 
    * 
    */
   public double getSigma() {
      return sigma;
   }


   /**
    * Sets the parameters μ and σ of this object.
    * 
    */
   protected void setParams (double mu, double sigma) {
      if (sigma <= 0)
         throw new IllegalArgumentException ("sigma <= 0");
      this.mu = mu;
      this.sigma = sigma;
   }

}