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From: "Kulpanowski, David" <DKulpanowski@leegov.com>
To: "user@commons.apache.org" <user@commons.apache.org>
Subject: [math] Poisson distribution to show how many ambulances are
 dispatched per hour
Thread-Topic: [math] Poisson distribution to show how many ambulances are
 dispatched per hour
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Date: Mon, 31 Aug 2015 16:21:23 +0000
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Hi:
I am working on a relatively simple project. I am attempting to generate a =
Poisson distribution for the number of ambulances that are dispatched. I ha=
ve looked at my database and determined the average number of ambulances di=
spatched is 9
How do I get a Poisson distribution to be generated using the Commons Math?

The output I am expecting to generate looks like this....

Likelihood of 1 ambulance dispatched is 0.005
Likelihood of 2 ambulances dispatched is 0.015
Likelihood of 3 ambulances dispatched is 0.034
Likelihood of 4 ambulances dispatched is 0.61
Likelihood of 5 ambulances dispatched is 0.091
Likelihood of 6 ambulances dispatched is 0.117
Etc.

This is probably a very simple programming question for many of you. But fo=
r me as a novice it is not easy.

So far, here is what I have using Commons Math;

import org.apache.commons.math3.distribution.PoissonDistribution;

public class poissonDistribution
{
       public static void main(String[] args)
       {
              PoissonDistribution ambulanceDistribution =3D new PoissonDist=
ribution(9);
              System.out.println(ambulanceDistribution);
       }
}

The console output is; "org.apache.commons.math3.distribution.PoissonDistri=
bution@27716f4"

I did try and take matters into my own hands and write the equation out (sh=
own below). But I have a very strong preference to use a method provided by=
 Commons Math. I am much more confident in Commons Math than my own abiliti=
es.

The following is my code. It works in a fashion, but I am not confident in =
it. Shown below is what I am currently using - but prefer to avoid using th=
is;
import java.lang.Math;
public class PoissonExperiment1
{
       public static void main(String[] args)
       {
              // c is the average number of calls per hour. This is a varia=
ble that is
              // derived from your database.
              double c =3D 9.0;
              // k is the number of expected calls we want to determine the=
 probability
              int k =3D 1;
              while (k <=3D 20)
              {
                     int factorialResult =3D 1;
                     for (int i =3D 1; i <=3D k; i++)
                     {
                           factorialResult =3D factorialResult * i;
                     }
                     double term1 =3D (Math.pow(Math.E, -c));
                     double term2 =3D Math.pow(c, k);
                     double numerator =3D term1 * term2;
                     double answer =3D numerator / factorialResult;
                     System.out.format("%10.3f:%n ", answer);
                     k++;
              }
       }
}


Thank you for your consideration and time,
David

David Kulpanowski
Database Analyst
Lee County Public Safety
PO Box 398
Fort Myers, FL 33902
DKulpanowski@Leegov.com
239-533-3962


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