src/main/java/org/apache/sysds/runtime/util/PoissonPRNGenerator.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 * 
 *   http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.sysds.runtime.util;

import org.apache.commons.math3.distribution.PoissonDistribution;
import org.apache.commons.math3.random.SynchronizedRandomGenerator;
import org.apache.commons.math3.random.Well1024a;


/**
 * Class that can generate a stream of random numbers from Poisson
 * distribution with specified mean. 
 */


public class PoissonPRNGenerator extends PRNGenerator
{
	private PoissonDistribution _pdist = null;
	private double _mean = Double.NaN;
	private long seed;
	
	public PoissonPRNGenerator() {
		// default mean and default seed
		super();
		_mean = 1.0;
		setup(_mean, seed);
	}
	
	public PoissonPRNGenerator(double mean) {
		// default seed
		super();
		_mean = mean;
		setup(_mean, seed);
	}

	public void setup(double mean, long sd) {
		seed = sd;
		SynchronizedRandomGenerator srg = new SynchronizedRandomGenerator(new Well1024a());
		srg.setSeed(seed);
		_pdist = new PoissonDistribution(srg, _mean, PoissonDistribution.DEFAULT_EPSILON, PoissonDistribution.DEFAULT_MAX_ITERATIONS);
	}
	
	@Override
	public void setSeed(long sd) {
		setup(_mean, sd);
	}
	
	public void setMean(double mean) {
		setup(mean, seed);
	}
	
	@Override
	public double nextDouble() {
		return _pdist.sample();
	}
}