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 &le; 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    }