cern.jet.random
Class AbstractDistribution

java.lang.Object
  cern.colt.PersistentObject
      cern.jet.random.AbstractDistribution

All Implemented Interfaces:

DoubleFunction, IntFunction, java.io.Serializable, java.lang.Cloneable

Direct Known Subclasses:

AbstractContinousDistribution

public abstract class AbstractDistribution
extends PersistentObject
implements DoubleFunction, IntFunction

Abstract base class for all random distributions. A subclass of this class need to override method nextDouble() and, in rare cases, also nextInt().

Currently all subclasses use a uniform pseudo-random number generation engine and transform its results to the target distribution. Thus, they expect such a uniform engine upon instance construction.

MersenneTwister is recommended as uniform pseudo-random number generation engine, since it is very strong and at the same time quick. makeDefaultGenerator() will conveniently construct and return such a magic thing. You can also, for example, use cern.jet.random.engine.DRand, a quicker (but much weaker) uniform random number generation engine. Of course, you can also use other strong uniform random number generation engines. Paul Houle's RngPack package contains some such beasts; Ranecu, Ranecu and Ranlux are strong well analyzed research grade uniform pseudo-random number generators with known periods. More info on RngPack can be found here.

Ressources on the Web:

Check the Web version of the CERN Data Analysis Briefbook . This will clarify the definitions of most distributions.

Also consult the StatSoft Electronic Textbook - the definite web book.

Other useful ressources:

Another site and yet another site describing the definitions of several distributions.

You may want to check out a Glossary of Statistical Terms.

The GNU Scientific Library contains an extensive (but hardly readable) list of definition of distributions.

Use this Web interface to plot all sort of distributions.

Even more ressources: Internet glossary of Statistical Terms, a text book, another text book.

Finally, a good link list Statistics on the Web.

Version:

1.0, 09/24/99

Author:

wolfgang.hoschek@cern.ch

See Also:

cern.jet.random.engine, edu.cornell.lassp.houle.RngPack, cern.jet.random.engine.Benchmark, cern.jet.random.Benchmark, Serialized Form

Method Summary

double	apply(double dummy) Equivalent to nextDouble().
int	apply(int dummy) Equivalent to nextInt().
java.lang.Object	clone() Returns a deep copy of the receiver; the copy will produce identical sequences.
static RandomElement	makeDefaultGenerator() Constructs and returns a new uniform random number generation engine seeded with the current time.
abstract double	nextDouble() Returns a random number from the distribution.
int	nextInt() Returns a random number from the distribution; returns (int) Math.round(nextDouble()).

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

apply

public double apply(double dummy)

Equivalent to nextDouble(). This has the effect that distributions can now be used as function objects, returning a random number upon function evaluation.

Specified by:

apply in interface DoubleFunction

Parameters:

dummy - argument passed to the function.

Returns:

the result of the function.

apply

public int apply(int dummy)

Equivalent to nextInt(). This has the effect that distributions can now be used as function objects, returning a random number upon function evaluation.

Specified by:

apply in interface IntFunction

Parameters:

dummy - argument passed to the function.

Returns:

the result of the function.

clone

public java.lang.Object clone()

Returns a deep copy of the receiver; the copy will produce identical sequences. After this call has returned, the copy and the receiver have equal but separate state.

Overrides:

clone in class PersistentObject

Returns:

a copy of the receiver.

nextDouble

public abstract double nextDouble()

Returns a random number from the distribution.

nextInt

public int nextInt()

Returns a random number from the distribution; returns (int) Math.round(nextDouble()). Override this method if necessary.

makeDefaultGenerator

public static RandomElement makeDefaultGenerator()

Constructs and returns a new uniform random number generation engine seeded with the current time. Currently this is MersenneTwister.