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


/**
 * This class implements random variate generators for the 
 * triangular distribution. Its  density is
 * 
 * 

 * 

 * 
 * 
 * 
 * 
 * 
 * 
 * 
 * 
 * 
 * 
 * 
 * 
 * 
 * 
f (x) =
2(x - a)/[(b - a)(m - a)]
         for a <= x <= m,
f (x) =
2(b - x)/[(b - a)(b - m)]
         for m <= x <= b,
f (x) =
0
         elsewhere,
 * 

 * where 
 * a <= m <= b (see, e.g.,).
 * 
 * 

 * The (non-static) nextDouble method simply calls inverseF on the
 * distribution.
 * 
 */
public class TriangularGen extends RandomVariateGen  {
   private double a;
   private double b;
   private double m;


   /**
    * Creates a triangular random variate generator over the interval
    * (a, b), with parameter m, using stream s.
    * 
    */
   public TriangularGen (RandomStream s, double a, double b, double m)  {
      super (s, new TriangularDist(a, b, m));
      setParams (a, b, m);
   }


   /**
    * Creates a triangular random variate generator over the interval
    *   (0, 1), with parameter m, using stream s.
    * 
    */
   public TriangularGen (RandomStream s, double m)  {
      this (s, 0.0, 1.0, m);
   }

 
   /**
    * Creates a new generator for the triangular distribution
    *  dist and stream s.
    * 
    */
   public TriangularGen (RandomStream s, TriangularDist dist)  {
      super (s, dist);
      if (dist != null)
         setParams (dist.getA(), dist.getB(), dist.getM());
   }

   
   /**
    * Generates a new variate from the triangular distribution with parameters
    *   a = a, b = b and m = m and stream s,
    *    using inversion.
    * 
    */
   public static double nextDouble (RandomStream s, double a, 
                                    double b, double m)  {
       // the code is taken and adapted from unuran
       // file /distributions/c_triangular_gen.c
       return TriangularDist.inverseF (a, b, m, s.nextDouble());
   }
      

   /**
    * Returns the value of a for this object.
    * 
    */
   public double getA() {
      return a;
   }
      

   /**
    * Returns the value of b for this object.
    * 
    */
   public double getB() {
      return b;
   }
      

   /**
    * Returns the value of m for this object.
    * 
    * 
    */
   public double getM() {
      return m;
   }
      

   /**
    * Sets the value of the parameters a, b and m for this object.
    * 
    */
   private void setParams (double a, double b, double m) {
      if ((a == 0.0 && b == 1.0) && (m < 0 || m > 1))
         throw new IllegalArgumentException ("m is not in [0,1]");
      else if (a >= b)
         throw new IllegalArgumentException ("a >= b");
      else if (m < a || m > b) 
         throw new IllegalArgumentException ("m is not in [a,b]");
      this.a = a;
      this.b = b;
      this.m = m;
   }
      
}