Commons Math example source code file (BinomialDistributionImpl.java)

This example Commons Math source code file (BinomialDistributionImpl.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Commons Math tags/keywords

abstractintegerdistribution, binomialdistribution, binomialdistributionimpl, binomialdistributionimpl, deprecated, deprecated, io, mathexception, mathexception, override, override, serializable

The Commons Math BinomialDistributionImpl.java source code

/*
 * 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 java.io.Serializable;

import org.apache.commons.math.MathException;
import org.apache.commons.math.MathRuntimeException;
import org.apache.commons.math.special.Beta;

/**
 * The default implementation of {@link BinomialDistribution}.
 *
 * @version $Revision: 920852 $ $Date: 2010-03-09 07:53:44 -0500 (Tue, 09 Mar 2010) $
 */
public class BinomialDistributionImpl extends AbstractIntegerDistribution
        implements BinomialDistribution, Serializable {

    /** Serializable version identifier */
    private static final long serialVersionUID = 6751309484392813623L;

    /** The number of trials. */
    private int numberOfTrials;

    /** The probability of success. */
    private double probabilityOfSuccess;

    /**
     * Create a binomial distribution with the given number of trials and
     * probability of success.
     *
     * @param trials the number of trials.
     * @param p the probability of success.
     */
    public BinomialDistributionImpl(int trials, double p) {
        super();
        setNumberOfTrialsInternal(trials);
        setProbabilityOfSuccessInternal(p);
    }

    /**
     * Access the number of trials for this distribution.
     *
     * @return the number of trials.
     */
    public int getNumberOfTrials() {
        return numberOfTrials;
    }

    /**
     * Access the probability of success for this distribution.
     *
     * @return the probability of success.
     */
    public double getProbabilityOfSuccess() {
        return probabilityOfSuccess;
    }

    /**
     * Change the number of trials for this distribution.
     *
     * @param trials the new number of trials.
     * @throws IllegalArgumentException if <code>trials is not a valid
     *             number of trials.
     * @deprecated as of 2.1 (class will become immutable in 3.0)
     */
    @Deprecated
    public void setNumberOfTrials(int trials) {
        setNumberOfTrialsInternal(trials);
    }
    /**
     * Change the number of trials for this distribution.
     *
     * @param trials the new number of trials.
     * @throws IllegalArgumentException if <code>trials is not a valid
     *             number of trials.
     */
    private void setNumberOfTrialsInternal(int trials) {
        if (trials < 0) {
            throw MathRuntimeException.createIllegalArgumentException(
                    "number of trials must be non-negative ({0})", trials);
        }
        numberOfTrials = trials;
    }

    /**
     * Change the probability of success for this distribution.
     *
     * @param p the new probability of success.
     * @throws IllegalArgumentException if <code>p is not a valid
     *             probability.
     * @deprecated as of 2.1 (class will become immutable in 3.0)
     */
    @Deprecated
    public void setProbabilityOfSuccess(double p) {
        setProbabilityOfSuccessInternal(p);
    }
    /**
     * Change the probability of success for this distribution.
     *
     * @param p the new probability of success.
     * @throws IllegalArgumentException if <code>p is not a valid
     *             probability.
     */
    private void setProbabilityOfSuccessInternal(double p) {
        if (p < 0.0 || p > 1.0) {
            throw MathRuntimeException.createIllegalArgumentException(
                    "{0} out of [{1}, {2}] range", p, 0.0, 1.0);
        }
        probabilityOfSuccess = p;
    }

    /**
     * Access the domain value lower bound, based on <code>p, used to
     * bracket a PDF root.
     *
     * @param p the desired probability for the critical value
     * @return domain value lower bound, i.e. P(X < <i>lower bound) <
     *         <code>p
     */
    @Override
    protected int getDomainLowerBound(double p) {
        return -1;
    }

    /**
     * Access the domain value upper bound, based on <code>p, used to
     * bracket a PDF root.
     *
     * @param p the desired probability for the critical value
     * @return domain value upper bound, i.e. P(X < <i>upper bound) >
     *         <code>p
     */
    @Override
    protected int getDomainUpperBound(double p) {
        return numberOfTrials;
    }

    /**
     * For this distribution, X, this method returns P(X ? x).
     *
     * @param x the value at which the PDF is evaluated.
     * @return PDF for this distribution.
     * @throws MathException if the cumulative probability can not be computed
     *             due to convergence or other numerical errors.
     */
    @Override
    public double cumulativeProbability(int x) throws MathException {
        double ret;
        if (x < 0) {
            ret = 0.0;
        } else if (x >= numberOfTrials) {
            ret = 1.0;
        } else {
            ret = 1.0 - Beta.regularizedBeta(getProbabilityOfSuccess(),
                    x + 1.0, numberOfTrials - x);
        }
        return ret;
    }

    /**
     * For this distribution, X, this method returns P(X = x).
     *
     * @param x the value at which the PMF is evaluated.
     * @return PMF for this distribution.
     */
    public double probability(int x) {
        double ret;
        if (x < 0 || x > numberOfTrials) {
            ret = 0.0;
        } else {
            ret = Math.exp(SaddlePointExpansion.logBinomialProbability(x,
                    numberOfTrials, probabilityOfSuccess,
                    1.0 - probabilityOfSuccess));
        }
        return ret;
    }

    /**
     * For this distribution, X, this method returns the largest x, such that
     * P(X ? x) ? <code>p.
     * <p>
     * Returns <code>-1 for p=0 and Integer.MAX_VALUE for
     * p=1.
     * </p>
     *
     * @param p the desired probability
     * @return the largest x such that P(X ? x) <= p
     * @throws MathException if the inverse cumulative probability can not be
     *             computed due to convergence or other numerical errors.
     * @throws IllegalArgumentException if p < 0 or p > 1
     */
    @Override
    public int inverseCumulativeProbability(final double p)
            throws MathException {
        // handle extreme values explicitly
        if (p == 0) {
            return -1;
        }
        if (p == 1) {
            return Integer.MAX_VALUE;
        }

        // use default bisection impl
        return super.inverseCumulativeProbability(p);
    }
}