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From "Gilles (JIRA)" <j...@apache.org>
Subject [jira] [Resolved] (MATH-823) Distribution classes should allow randomData to be configured via constructor or setter
Date Fri, 20 Jul 2012 00:52:34 GMT

     [ https://issues.apache.org/jira/browse/MATH-823?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Gilles resolved MATH-823.
-------------------------

       Resolution: Fixed
    Fix Version/s: 3.1

A "RandomGenerator" instance can now be passed at construction (revision 1363604).
Please note that the "RandomDataImpl" instance has been deprecated.
                
> Distribution classes should allow randomData to be configured via constructor or setter
> ---------------------------------------------------------------------------------------
>
>                 Key: MATH-823
>                 URL: https://issues.apache.org/jira/browse/MATH-823
>             Project: Commons Math
>          Issue Type: Improvement
>    Affects Versions: 3.0
>            Reporter: Steve Phelps
>            Assignee: Gilles
>            Priority: Minor
>             Fix For: 3.1
>
>
> In my application I would like to represent several different probability distributions
using polymorphism - see example below.  At compile-time the distributions are declared of
type RealDistribution.  These distributions are then configured with concrete classes at run-time
using, e.g. dependency injection.  However, because there is no way to configure the underlying
PRNG -- ie the randomData field of these distributions, there is a danger of introducing correlations
into the random number streams through poor seed management.  If I have dozens of distributions,
each configured automatically with a new RandomDataImpl() then there is the possibility that
some of these streams will share the same seed value introducing spurious correlations.  
> One solution to this would be to explicitly manage seed values for every distribution
in my simulation by calling reseedRandomGenerator().  However, this introduces unnecessary
complexity and dependencies throughout my code.  A far simpler solution for my use case would
be to configure all the distributions in my simulation to use the same singleton instance
of RandomDataImpl for their randomData field (eg using dependency injection), thus ensuring
truly independent distributions -  however currently the API does not support this.
>  
> Could the Distribution classes be refactored to allow the randomData field to be configured,
eg through setters or via the constructor?   This would be similar to the design of the distribution
classes provided by the CERN colt library, which I believe offers more flexibility in this
respect.  It would also be ideal, IMHO, if the Distribution objects were POJOs with zero-arg
constructors, which would then allow them to be configured using a dependency-injection framework.
> public class Simulation {
> 	RealDistribution interArrivalTimeDistribution;
> 	
> 	RealDistribution sizeDistribution;
> 	
> 	double t;
> 	
> 	public void run() {
> 		t = 0;
> 		while (true) {
> 			t += interArrivalTimeDistribution.sample();
> 			double magnitude = sizeDistribution.sample();
> 			System.out.println(t  + "\t" + magnitude);
> 		}
> 	}
> 	public RealDistribution getInterArrivalTimeDistribution() {
> 		return interArrivalTimeDistribution;
> 	}
> 	public void setInterArrivalTimeDistribution(RealDistribution interArrivalTimes) {
> 		this.interArrivalTimeDistribution = interArrivalTimes;
> 	}
> 	public RealDistribution getSizeDistribution() {
> 		return sizeDistribution;
> 	}
> 	public void setSizeDistribution(RealDistribution xsizeDistribution) {
> 		this.sizeDistribution = sizeDistribution;
> 	}
> 	
> 	
> }

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