// ============================================================================
// Copyright 2006-2012 Daniel W. Dyer
//
// 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 org.uncommons.maths.demo;
import java.util.HashMap;
import java.util.Map;
import java.util.Random;
import org.uncommons.maths.random.ExponentialGenerator;
/**
* @author Daniel Dyer
*/
class ExponentialDistribution extends ProbabilityDistribution
{
private final double rate;
public ExponentialDistribution(double rate)
{
this.rate = rate;
}
protected ExponentialGenerator createValueGenerator(Random rng)
{
return new ExponentialGenerator(rate, rng);
}
public Map<Double, Double> getExpectedValues()
{
Map<Double, Double> values = new HashMap<Double, Double>();
double p;
double x = 0;
do
{
p = getExpectedProbability(x);
values.put(x, p);
x += (1 / (2 * rate));
} while (p > 0.001);
return values;
}
/**
* This is the probability density function for the Exponential
* distribution.
*/
private double getExpectedProbability(double x)
{
if (x < 0)
{
return 0;
}
else
{
return rate * Math.exp(-rate * x);
}
}
public double getExpectedMean()
{
return Math.pow(rate, -1);
}
public double getExpectedStandardDeviation()
{
return Math.sqrt(Math.pow(rate, -2));
}
public String getDescription()
{
return "Exponential Distribution (\u03bb = " + rate + ")";
}
public boolean isDiscrete()
{
return false;
}
}