statistics.distribution.ExponentialDistribution.java Source code

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Here is the source code for statistics.distribution.ExponentialDistribution.java

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/**
 * Copyright 2011 Amir Moulavi (amir.moulavi@gmail.com)
 *
 *    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.
 */
package statistics.distribution;

import org.jfree.chart.ChartFactory;
import org.jfree.chart.JFreeChart;
import org.jfree.chart.plot.PlotOrientation;
import org.jfree.data.xy.XYDataset;
import org.jfree.data.xy.XYSeries;
import org.jfree.data.xy.XYSeriesCollection;

import java.util.Random;

/**
 * 
 * @author Amir Moulavi
 * @date 2011-04-02
 * 
 * F(u) = -ln(1-u)/   for (0 < u <1)
 */

public class ExponentialDistribution implements Distribution {

    private double lambda;
    private Random random = new Random();
    private double minInterval;

    public ExponentialDistribution() {
        this.lambda = 1;
        this.minInterval = 10;
    }

    @Override
    public long getNextValue() {
        double re = (-1 / lambda) * Math.log(1 - random.nextDouble());
        re += minInterval;
        return (long) (1000 * re);
    }

    @Override
    public JFreeChart getChart() {
        JFreeChart chart = ChartFactory.createXYLineChart("Exponential Cumulative Distribution", "", "",
                getDataset(), PlotOrientation.VERTICAL, true, true, false);
        return chart;
    }

    @Override
    public void setParameters(String... params) {
        if (params.length >= 1) {
            minInterval = Double.parseDouble(params[0]);
        }
    }

    public void setMinInterval(double minInterval) {
        this.minInterval = minInterval;
    }

    private XYDataset getDataset() {
        XYSeriesCollection dataSet = new XYSeriesCollection();
        XYSeries xySeries = new XYSeries("CDF");
        double x = 0.0;
        for (int i = 0; i < 50; i++) {
            xySeries.add(x, CDF(x));
            x += 0.2;
        }
        dataSet.addSeries(xySeries);
        return dataSet;
    }

    private double CDF(double x) {
        return 1 - Math.exp(-1 * lambda * x);
    }

}