edu.cmu.tetrad.util.dist.Gamma Maven / Gradle / Ivy
///////////////////////////////////////////////////////////////////////////////
// For information as to what this class does, see the Javadoc, below. //
// Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, //
// 2007, 2008, 2009, 2010, 2014, 2015, 2022 by Peter Spirtes, Richard //
// Scheines, Joseph Ramsey, and Clark Glymour. //
// //
// This program is free software; you can redistribute it and/or modify //
// it under the terms of the GNU General Public License as published by //
// the Free Software Foundation; either version 2 of the License, or //
// (at your option) any later version. //
// //
// This program is distributed in the hope that it will be useful, //
// but WITHOUT ANY WARRANTY; without even the implied warranty of //
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the //
// GNU General Public License for more details. //
// //
// You should have received a copy of the GNU General Public License //
// along with this program; if not, write to the Free Software //
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA //
///////////////////////////////////////////////////////////////////////////////
package edu.cmu.tetrad.util.dist;
import edu.cmu.tetrad.util.RandomUtil;
/**
* Wraps a chi square distribution for purposes of drawing random samples. Methods are provided to allow parameters to
* be manipulated in an interface.
*
* @author josephramsey
*/
public class Gamma implements Distribution {
private static final long serialVersionUID = 23L;
private double alpha;
private double lambda;
private Gamma() {
this.alpha = .5;
this.lambda = .7;
}
/**
* Generates a simple exemplar of this class to test serialization.
*
* @return The exemplar.
*/
public static Gamma serializableInstance() {
return new Gamma();
}
public int getNumParameters() {
return 2;
}
public String getName() {
return "Gamma";
}
public void setParameter(int index, double value) {
if (index == 0) {
this.alpha = value;
} else if (index == 1) {
this.lambda = value;
}
throw new IllegalArgumentException();
}
public double getParameter(int index) {
if (index == 0) {
return this.alpha;
} else if (index == 1) {
return this.lambda;
}
throw new IllegalArgumentException();
}
public String getParameterName(int index) {
if (index == 0) {
return "Alpha";
} else if (index == 1) {
return "Lambda";
}
throw new IllegalArgumentException();
}
public double nextRandom() {
return RandomUtil.getInstance().nextGamma(this.alpha, this.lambda);
}
public String toString() {
return "Gamma(" + this.alpha + ", " + this.lambda + ")";
}
}