DistWeibull.java
package nl.tudelft.simulation.jstats.distributions;
import org.djutils.exceptions.Throw;
import nl.tudelft.simulation.jstats.streams.StreamInterface;
/**
* The Weibull distribution with a shape parameter α and a scale parameter β. For more information on this
* distribution see <a href="https://mathworld.wolfram.com/WeibullDistribution.html">
* https://mathworld.wolfram.com/WeibullDistribution.html </a>
* <p>
* Copyright (c) 2002-2024 Delft University of Technology, Jaffalaan 5, 2628 BX Delft, the Netherlands. All rights reserved. See
* for project information <a href="https://simulation.tudelft.nl/" target="_blank"> https://simulation.tudelft.nl</a>. The DSOL
* project is distributed under a three-clause BSD-style license, which can be found at
* <a href="https://https://simulation.tudelft.nl/dsol/docs/latest/license.html" target="_blank">
* https://https://simulation.tudelft.nl/dsol/docs/latest/license.html</a>.
* </p>
* @author <a href="https://www.linkedin.com/in/peterhmjacobs">Peter Jacobs </a>
* @author <a href="https://www.tudelft.nl/averbraeck">Alexander Verbraeck</a>
*/
public class DistWeibull extends DistContinuous
{
/** */
private static final long serialVersionUID = 1L;
/** alpha is the shape parameter α. */
private final double alpha;
/** beta is the scale parameter β. */
private final double beta;
/**
* constructs a new Weibull distribution.
* @param stream StreamInterface; the random number stream
* @param alpha double; the shape parameter α
* @param beta double; the scale parameter β
*/
public DistWeibull(final StreamInterface stream, final double alpha, final double beta)
{
super(stream);
Throw.when(alpha <= 0.0 || beta <= 0.0, IllegalArgumentException.class, "Error Weibull - alpha <= 0.0 or beta <= 0.0");
this.alpha = alpha;
this.beta = beta;
}
/** {@inheritDoc} */
@Override
public double draw()
{
return this.beta * Math.pow(-Math.log(this.stream.nextDouble()), 1.0d / this.alpha);
}
/** {@inheritDoc} */
@Override
public double getProbabilityDensity(final double x)
{
if (x > 0)
{
return this.alpha * Math.pow(this.beta, -this.alpha) * Math.pow(x, this.alpha - 1)
* Math.exp(-Math.pow(x / this.beta, this.alpha));
}
return 0.0;
}
/**
* Return the shape parameter α.
* @return double; the shape parameter α
*/
public double getAlpha()
{
return this.alpha;
}
/**
* Return the scale parameter β.
* @return double; the scale parameter β
*/
public double getBeta()
{
return this.beta;
}
/** {@inheritDoc} */
@Override
public String toString()
{
return "Weibull(" + this.alpha + "," + this.beta + ")";
}
}