/*
 * 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.commons.math.distribution;

import org.apache.commons.math.MathException;

/**
 * Interface representing the Poisson Distribution.
 * 
 * <p>
 * References:
 * <ul>
 * <li><a href="http://mathworld.wolfram.com/PoissonDistribution.html"> Poisson
 * distribution</a></li>
 * </ul>
 * </p>
 * 
 * @version $Revision$ $Date$
 */
public interface PoissonDistribution extends IntegerDistribution {

	/**
	 * Get the mean for the distribution.
	 * 
	 * @return the mean for the distribution.
	 */
	public double getMean();

	/**
	 * Set the mean for the distribution. The parameter value must be positive;
	 * otherwise an <code>IllegalArgument</code> is thrown.
	 * 
	 * @param p
	 *            the mean
	 * @throws IllegalArgumentException
	 *             if p &le; 0
	 */
	public void setMean(double p);

	/**
	 * Calculates the Poisson distribution function using a normal
	 * approximation.
	 * 
	 * @param x
	 *            the upper bound, inclusive
	 * @return the distribution function value calculated using a normal
	 *         approximation
	 * @throws MathException
	 *             if an error occurs computing the normal approximation
	 */
	public double normalApproximateProbability(int x) throws MathException;
}