001 /*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements. See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License. You may obtain a copy of the License at
008 *
009 * http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017 package org.apache.commons.math.distribution;
018
019 import org.apache.commons.math.MathException;
020
021 /**
022 * Interface representing the Poisson Distribution.
023 *
024 * <p>
025 * References:
026 * <ul>
027 * <li><a href="http://mathworld.wolfram.com/PoissonDistribution.html">
028 * Poisson distribution</a></li>
029 * </ul>
030 * </p>
031 *
032 * @version $Revision: 670469 $ $Date: 2008-06-23 04:01:38 -0400 (Mon, 23 Jun 2008) $
033 */
034 public interface PoissonDistribution extends IntegerDistribution {
035
036 /**
037 * Get the mean for the distribution.
038 *
039 * @return the mean for the distribution.
040 */
041 public double getMean();
042
043 /**
044 * Set the mean for the distribution.
045 * The parameter value must be positive; otherwise an
046 * <code>IllegalArgument</code> is thrown.
047 *
048 * @param p the mean
049 * @throws IllegalArgumentException if p ≤ 0
050 */
051 public void setMean(double p);
052
053 /**
054 * Calculates the Poisson distribution function using a normal approximation.
055 *
056 * @param x the upper bound, inclusive
057 * @return the distribution function value calculated using a normal approximation
058 * @throws MathException if an error occurs computing the normal approximation
059 */
060 public double normalApproximateProbability(int x) throws MathException;
061 }