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


/**
 * This class implements random variate generators for the 
 * logistic distribution. Its parameters are α and 
 * λ > 0.
 * Its density function is 
 * 
 * 

 * 

 * f (x) = λe-λ(x-α)/[(1 + e-λ(x-α))2] for  - ∞ < x < ∞.
 * 

 * The (non-static) nextDouble method simply calls inverseF on the
 * distribution.
 * 
 */
public class LogisticGen extends RandomVariateGen  {
   protected double alpha = -1.0;
   protected double lambda = -1.0;
    



   /**
    * Creates a logistic random variate generator with parameters
    *   α = alpha and λ = lambda,
    *   using stream s.
    * 
    */
   public LogisticGen (RandomStream s, double alpha, double lambda)  {
      super (s, new LogisticDist(alpha, lambda));
      setParams (alpha, lambda);
   }


   /**
    * Creates a logistic random variate generator with parameters
    *   
    * α = 0 and 
    * λ = 1,
    *   using stream s.
    * 
    */
   public LogisticGen (RandomStream s)  {
      this (s, 0.0, 1.0);
   }


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


   /**
    * Generates a new variate from the logistic distribution
    *    with parameters α = alpha and λ = lambda,
    *    using stream s.
    * 
    */
   public static double nextDouble (RandomStream s,
                                    double alpha, double lambda) {
      return  LogisticDist.inverseF (alpha, lambda, s.nextDouble());
   }



   /**
    * Returns the parameter α of this object.
    * 
    */
   public double getAlpha() {
      return alpha;
   }


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


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

}