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


/**
 * This class implements random variate generators for the 
 * hypergeometric distribution. Its mass function is
 * 
 * 

 * 

 * p(x) = nCr(m, x)nCr(l - m, k - x)/nCr(l, k)        for x = max(0, k - l + m),..., min(k, m)
 * 

 * where nCr(n, x) is the number of possible combinations when choosing
 * x elements among a set of n elements,
 * m, l and k are integers that satisfy 0 < m <= l and 
 * 0 < k <= l.
 * 
 * 

 * The generation method is inversion using the chop-down algorithm
 * 
 */
public class HypergeometricGen extends RandomVariateGenInt  {
   private int m;
   private int l;
   private int k;    



   /**
    * Creates a hypergeometric generator with
    *    parameters m = m, l = l and k = k,
    *    using stream s.
    * 
    */
   public HypergeometricGen (RandomStream s, int m, int l, int k)  {
      super (s, new HypergeometricDist (m, l, k));
      setParams (m, l, k);
   }


   /**
    * Creates a new generator for distribution dist,
    *     using stream s.
    * 
    */
   public HypergeometricGen (RandomStream s, HypergeometricDist dist)  {
      super (s, dist);
      if (dist != null)
         setParams (dist.getM(), dist.getL(), dist.getK());
   }


   /**
    * Generates a new variate from the hypergeometric distribution with
    *    parameters m = m, l = l and k = k,
    *    using stream s.
    * 
    */
   public static int nextInt (RandomStream s, int m, int l, int k) {
      return HypergeometricDist.inverseF (m, l, k, s.nextDouble());
   }


   /**
    * Returns the m associated with this object.
    * 
    */
   public int getM() {
      return m;
   }


   /**
    * Returns the l associated with this object.
    * 
    */
   public int getL() {
      return l;
   }


   /**
    * Returns the k associated with this object.
    * 
    * 
    */
   public int getK() {
      return k;
   }


   /**
    * Sets the parameter n and p of this object.
    * 
    */
   protected void setParams (int m, int l, int k) {
      if (l <= 0)
         throw new IllegalArgumentException ("l must be greater than 0");
      if (m <= 0 || m > l)
         throw new IllegalArgumentException ("m is invalid: 1<=m l)
         throw new IllegalArgumentException ("k is invalid: 1<=k