cern.jet.random.BreitWigner Maven / Gradle / Ivy

/*
Copyright (c) 1999 CERN - European Organization for Nuclear Research.
Permission to use, copy, modify, distribute and sell this software and its documentation for any purpose 
is hereby granted without fee, provided that the above copyright notice appear in all copies and 
that both that copyright notice and this permission notice appear in supporting documentation. 
CERN makes no representations about the suitability of this software for any purpose. 
It is provided "as is" without expressed or implied warranty.
*/
package cern.jet.random;

import cern.jet.random.engine.RandomEngine;
/**
 * BreitWigner (aka Lorentz) distribution; See the  math definition.
 * A more general form of the Cauchy distribution.
 * 
 * Instance methods operate on a user supplied uniform random number generator; they are unsynchronized. 
 * 
 * Static methods operate on a default uniform random number generator; they are synchronized.
 * 
 * Implementation: This is a port of RandBreitWigner used in CLHEP 1.4.0 (C++).
 *
 * @author [email protected]
 * @version 1.0, 09/24/99
 */
public class BreitWigner extends AbstractContinousDistribution {
	protected double mean;
	protected double gamma;
	protected double cut;

	// The uniform random number generated shared by all static methods.
	protected static BreitWigner shared = new BreitWigner(1.0,0.2,1.0,makeDefaultGenerator());
/**
 * Constructs a BreitWigner distribution.
 * @param cut cut==Double.NEGATIVE_INFINITY indicates "don't cut".
 */
public BreitWigner(double mean, double gamma, double cut, RandomEngine randomGenerator) {
	setRandomGenerator(randomGenerator);
	setState(mean, gamma, cut);
}
/**
 * Returns a random number from the distribution.
 */
public double nextDouble() {
	return nextDouble(mean, gamma, cut);
}
/**
 * Returns a random number from the distribution; bypasses the internal state.
 * @param cut cut==Double.NEGATIVE_INFINITY indicates "don't cut".
 */
public double nextDouble(double mean,double gamma,double cut) {
	double val, rval, displ;

	if (gamma == 0.0) return mean;
	if (cut==Double.NEGATIVE_INFINITY) { // don't cut
		rval = 2.0*randomGenerator.raw()-1.0;
		displ = 0.5*gamma*Math.tan(rval*(Math.PI/2.0));
		return mean + displ;
	}
	else {
		val = Math.atan(2.0*cut/gamma);
		rval = 2.0*randomGenerator.raw()-1.0;
		displ = 0.5*gamma*Math.tan(rval*val);

		return mean + displ;
	}
}
/**
 * Sets the mean, gamma and cut parameters.
 * @param cut cut==Double.NEGATIVE_INFINITY indicates "don't cut".
 */
public void setState(double mean, double gamma, double cut) {
	this.mean = mean;
	this.gamma = gamma;
	this.cut = cut;
}
/**
 * Returns a random number from the distribution.
 * @param cut cut==Double.NEGATIVE_INFINITY indicates "don't cut".
 */
public static double staticNextDouble(double mean,double gamma,double cut) {
	synchronized (shared) {
		return shared.nextDouble(mean,gamma,cut);
	}
}
/**
 * Returns a String representation of the receiver.
 */
public String toString() {
	return this.getClass().getName()+"("+mean+","+gamma+","+cut+")";
}
/**
 * Sets the uniform random number generated shared by all static methods.
 * @param randomGenerator the new uniform random number generator to be shared.
 */
private static void xstaticSetRandomGenerator(RandomEngine randomGenerator) {
	synchronized (shared) {
		shared.setRandomGenerator(randomGenerator);
	}
}
}