desmoj.core.dist.ContDistBeta.java Source code

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Here is the source code for desmoj.core.dist.ContDistBeta.java

Source

package desmoj.core.dist;

import org.apache.commons.math.MathException;

import desmoj.core.simulator.Model;

/**
 * Distribution returning Beta distributed double values.
 * 
 * @version DESMO-J, Ver. 2.3.5 copyright (c) 2013
 * @author Peter Wueppen
 * 
 *         Licensed 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.
 * 
 */

public class ContDistBeta extends ContDist {

    /**
     * Distribution specific parameter alpha
     */
    protected double alpha;

    /**
     * Distribution specific parameter beta
     */
    protected double beta;

    /**
     * Creates a stream of pseudo random numbers following a Beta distribution.
     * The specific parameters alpha and beta have to be given here at creation
     * time.
     * 
     * @param owner
     *            Model : The distribution's owner
     * @param name
     *            java.lang.String : The distribution's name
     * @param alpha
     *            double: Distribution specific parameter alpha
     * @param beta
     *            double : Distribution specific parameter beta
     * @param showInReport
     *            boolean : Flag for producing reports
     * @param showInTrace
     *            boolean : Flag for producing trace output
     */
    public ContDistBeta(Model owner, String name, double alpha, double beta, boolean showInReport,
            boolean showInTrace) {
        super(owner, name, showInReport, showInTrace);
        this.alpha = alpha;
        this.beta = beta;
        // TODO Auto-generated constructor stub
    }

    /**
     * Creates the default reporter for the BetaDist distribution.
     * 
     * @return Reporter : The reporter for the BetaDist distribution
     * @see desmoj.core.report.ContDistBetaReporter
     */
    public desmoj.core.report.Reporter createReporter() {

        return new desmoj.core.report.ContDistBetaReporter(this);

    }

    /**
     * 
     * @return double : Distribution specific shape parameter alpha
     */
    public double getAlpha() {

        return alpha;
    }

    /**
     * 
     * @return double : Distribution specific scale parameter beta
     */
    public double getBeta() {

        return beta;

    }

    /**
     * Returns the next sample from this distribution. The value depends upon
     * the seed, the number of values taken from the stream by using this method
     * before and the alpha and beta parameters specified for this distribution.
     * 
     * @return Double : The next Beta distributed sample from this distribution.
     */
    public Double sample() {

        double newSample = -1; //
        double randomNumber1 = randomGenerator.nextDouble();
        double randomNumber2 = randomGenerator.nextDouble();
        org.apache.commons.math.distribution.GammaDistribution gammadist1 = new org.apache.commons.math.distribution.GammaDistributionImpl(
                alpha, 1);
        org.apache.commons.math.distribution.GammaDistribution gammadist2 = new org.apache.commons.math.distribution.GammaDistributionImpl(
                beta, 1);
        incrementObservations(); // increase count of samples

        if (isAntithetic()) {

            try {
                double gammaval1 = gammadist1.inverseCumulativeProbability(1 - randomNumber1);
                double gammaval2 = gammadist2.inverseCumulativeProbability(1 - randomNumber2);
                newSample = gammaval1 / (gammaval1 + gammaval2);
            } catch (MathException e) {
            }
        } else {
            try {
                double gammaval1 = gammadist1.inverseCumulativeProbability(randomNumber1);
                double gammaval2 = gammadist2.inverseCumulativeProbability(randomNumber2);
                newSample = gammaval1 / (gammaval1 + gammaval2);
            } catch (MathException e) {
            }
        }

        if (this.currentlySendTraceNotes())
            this.traceLastSample(Double.toString(newSample));

        return newSample;
    }
}