ErlangDist.java

/*
 * Class:        ErlangDist
 * Description:  Erlang distribution
 * Environment:  Java
 * Software:     SSJ
 * Copyright (C) 2001  Pierre L'Ecuyer and Universite de Montreal
 * Organization: DIRO, Universite de Montreal
 * @author
 * @since
 *
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */
package umontreal.ssj.probdist;

public class ErlangDist extends GammaDist {

   public ErlangDist(int k) {
      super(k);
   }

   public ErlangDist(int k, double lambda) {
      super(k, lambda);
   }

   public static double density(int k, double lambda, double x) {
      return density((double) k, lambda, x);
   }

   public static double cdf(int k, double lambda, int d, double x) {
      return cdf((double) k, d, lambda * x);
   }

   public static double barF(int k, double lambda, int d, double x) {
      return barF((double) k, d, lambda * x);
   }

   public static double inverseF(int k, double lambda, int d, double u) {
      return inverseF((double) k, lambda, d, u);
   }

   public static double[] getMLE(double[] x, int n) {
      double parameters[] = GammaDist.getMLE(x, n);
      parameters[0] = Math.round(parameters[0]);
      return parameters;
   }

   public static ErlangDist getInstanceFromMLE(double[] x, int n) {
      double parameters[] = getMLE(x, n);
      return new ErlangDist((int) parameters[0], parameters[1]);
   }

   public static double getMean(int k, double lambda) {
      if (k <= 0)
         throw new IllegalArgumentException("k <= 0");
      if (lambda <= 0.0)
         throw new IllegalArgumentException("lambda <= 0");
      return (k / lambda);
   }

   public static double getVariance(int k, double lambda) {
      if (k <= 0)
         throw new IllegalArgumentException("k <= 0");
      if (lambda <= 0.0)
         throw new IllegalArgumentException("lambda <= 0");
 
      return (k / (lambda * lambda));
   }

   public static double getStandardDeviation(int k, double lambda) {
      if (k <= 0)
         throw new IllegalArgumentException("k <= 0");
      if (lambda <= 0.0)
         throw new IllegalArgumentException("lambda <= 0");
 
      return (Math.sqrt(k) / lambda);
   }

   public int getK() {
      return (int) getAlpha();
   }

   public void setParams(int k, double lambda, int d) {
      super.setParams(k, lambda, d);
   }

   public double[] getParams() {
      return super.getParams();
   }

   public String toString() {
      return getClass().getSimpleName() + " : k = " + (int) super.getAlpha() + ", lambda = " + super.getLambda();
   }
 
}