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    1   /*
    2    * Copyright 2004 The Apache Software Foundation.
    3    *
    4    * Licensed under the Apache License, Version 2.0 (the "License");
    5    * you may not use this file except in compliance with the License.
    6    * You may obtain a copy of the License at
    7    *
    8    *      http://www.apache.org/licenses/LICENSE-2.0
    9    *
    10   * Unless required by applicable law or agreed to in writing, software
    11   * distributed under the License is distributed on an "AS IS" BASIS,
    12   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    13   * See the License for the specific language governing permissions and
    14   * limitations under the License.
    15   */
    16  package org.apache.commons.math.distribution;
    17
    18  import org.apache.commons.math.MathException;
    19
    20  /***
    21   * Interface representing the Poisson Distribution.
    22   *
    23   * <p>
    24   * References:
    25   * <ul>
    26   * <li><a href="http://mathworld.wolfram.com/PoissonDistribution.html">
    27   * Poisson distribution</a></li>
    28   * </ul>
    29   * </p>
    30   *
    31   * @version $Revision: 1.2 $ $Date: 2004/11/07 20:39:15 $
    32   */
    33  public interface PoissonDistribution extends IntegerDistribution {
    34
    35      /***
    36       * Get the mean for the distribution.
    37       *
    38       * @return the mean for the distribution.
    39       */
    40      public double getMean();
    41
    42      /***
    43       * Set the mean for the distribution.
    44       * The parameter value must be positive; otherwise an
    45       * <code>IllegalArgument</code> is thrown.
    46       *
    47       * @param p the mean
    48       * @throws IllegalArgumentException if p &le; 0
    49       */
    50      public void setMean(double p);
    51
    52      /***
    53       * Calculates the Poisson distribution function using a normal approximation.
    54       *
    55       * @param x the upper bound, inclusive
    56       * @return the distribution function value calculated using a normal approximation
    57       * @throws MathException if an error occurs computing the normal approximation
    58       */
    59      public double normalApproximateProbability(int x) throws MathException;
    60  }