Package nl.tudelft.simulation.jstats.distributions

Class DistGamma

java.lang.Object

nl.tudelft.simulation.jstats.distributions.Dist

nl.tudelft.simulation.jstats.distributions.DistContinuous

nl.tudelft.simulation.jstats.distributions.DistGamma

All Implemented Interfaces:

Serializable

public class DistGamma
extends DistContinuous

The Gamma distribution. For more information on this distribution see https://mathworld.wolfram.com/GammaDistribution.html
The parameters are not rate-related, but average-related, so the mean is shape*scale (or αθ), and the variance is αθ².

Copyright (c) 2002-2023 Delft University of Technology, Jaffalaan 5, 2628 BX Delft, the Netherlands. All rights reserved. See for project information https://simulation.tudelft.nl. The DSOL project is distributed under a three-clause BSD-style license, which can be found at https://https://simulation.tudelft.nl/dsol/docs/latest/license.html.

Author:

Peter Jacobs , Alexander Verbraeck

See Also:

Serialized Form

Field Summary

Fields inherited from class nl.tudelft.simulation.jstats.distributions.Dist

stream

Constructor Summary

Constructors

Constructor	Description
DistGamma(StreamInterface stream, double shape, double scale)	constructs a new gamma distribution.

Method Summary

Modifier and Type	Method	Description
double	draw()	draws the next stream value according to the probability of this this distribution.
double	getProbabilityDensity(double x)	returns the probability density value of a value x.
double	getScale()
double	getShape()
String	toString()

Methods inherited from class nl.tudelft.simulation.jstats.distributions.Dist

getStream, setStream

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

DistGamma

public DistGamma(StreamInterface stream,
                 double shape,
                 double scale)

constructs a new gamma distribution. The gamma distribution represents the time to complete some task, e.g. customer service or machine repair. The parameters are not rate-related, but average-related, so the mean is shape*scale (or αθ or kθ), and the variance is αθ².

Parameters:

stream - StreamInterface; the random number stream

shape - double; is the shape parameter > 0, also known as α or k

scale - double; is the scale parameter> 0, also known as θ

Throws:

IllegalArgumentException - when shape <= 0.0 or scale <= 0.0

Method Detail

draw

public double draw()

draws the next stream value according to the probability of this this distribution.

Specified by:

draw in class DistContinuous

Returns:

the next double value drawn.

getProbabilityDensity

public double getProbabilityDensity(double x)

returns the probability density value of a value x.

Specified by:

getProbabilityDensity in class DistContinuous

Parameters:

x - double; the value for which the density function needs to be calculated

Returns:

double; the probability density for value x

getShape

public double getShape()

Returns:

alpha

getScale

public double getScale()

Returns:

beta

toString

public String toString()

Overrides:

toString in class Object