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


/**
 * This class implements random variate generators for the 
 * Fisher F distribution with n and m
 * degrees of freedom, where n and m are positive integers.
 * The density function of this distribution is
 * 
 * 

 * 

 * f (x) = Γ((n + m)/2)nn/2mm/2/[Γ(n/2)Γ(m/2)]x(n-2)/2/(m + nx)(n+m)/2,         for x > 0.
 * 

 * 
 */
public class FisherFGen extends RandomVariateGen  {
   protected int    n = -1;
   protected int    m = -1;




   /**
    * Creates a Fisher F random variate generator with 
    *  n and m degrees of freedom, using stream s.
    * 
    */
   public FisherFGen (RandomStream s, int n, int m)  {
      super (s, new FisherFDist(n, m));
      setParams (n, m);
      }


   /**
    * Creates a new generator for the distribution dist,
    *      using stream s.
    * 
    */
   public FisherFGen (RandomStream s, FisherFDist dist)  {
      super (s, dist);
      if (dist != null)
         setParams (dist.getN(), dist.getM());
   }

 
   /**
    * Generates a variate from the Fisher F distribution with
    *    n and m degrees of freedom, using stream s.
    * 
    */
   public static double nextDouble (RandomStream s, int n, int m) {
      return FisherFDist.inverseF (n, m, 15, s.nextDouble());
   }


   /**
    * Returns the parameter n of this object.
    * 
    */
   public int getN() {
      return n;
   }
   


   /**
    * Returns the parameter p of this object.
    * 
    * 
    */
   public int getM() {
      return m;
   }
   


   /**
    * Sets the parameters n and m of this object.
    * 
    */
   protected void setParams (int n, int m) {
      if (m <= 0)
         throw new IllegalArgumentException ("m <= 0");
      if (n <= 0)
         throw new IllegalArgumentException ("n <= 0");
      this.m = m;
      this.n = n;
   }

}