/*
* DiscreteUniformDistribution.java
*
* Copyright (c) 2002-2015 Alexei Drummond, Andrew Rambaut and Marc Suchard
*
* This file is part of BEAST.
* See the NOTICE file distributed with this work for additional
* information regarding copyright ownership and licensing.
*
* BEAST is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* BEAST is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with BEAST; if not, write to the
* Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
* Boston, MA 02110-1301 USA
*/
package dr.math.distributions;
import dr.math.UnivariateFunction;
/**
* Created by mandevgill on 11/15/14.
*/
public class DiscreteUniformDistribution implements Distribution {
public DiscreteUniformDistribution(double lower, double upper) {
this.lower = lower;
this.upper = upper;
this.n = upper - lower + 1;
}
public double pdf(double x) {
if (x < lower) {
return 0;
} else if (x > upper) {
return 0;
} else {
return 1 / n;
}
}
public double logPdf(double x) {
/*
if (x < 0) return Double.NEGATIVE_INFINITY;
double r = -1 * (mean*mean) / (mean - stdev*stdev);
double p = mean / (stdev*stdev);
return Math.log(Math.pow(1-p,x)) + Math.log(Math.pow(p, r)) + GammaFunction.lnGamma(r + x) - GammaFunction.lnGamma(r) - GammaFunction.lnGamma(x+1);
*/
if (x < lower) {
return Double.NEGATIVE_INFINITY;
} else if (x > upper) {
return Double.NEGATIVE_INFINITY;
} else {
return -Math.log(n);
}
}
public double cdf(double x) {
return (x - lower + 1) / n;
}
public double quantile(double y) {
// fill in
return Double.NaN;
}
public double mean() {
return (lower + upper) / 2;
}
public double variance() {
return (n * n - 1) / 12;
}
public UnivariateFunction getProbabilityDensityFunction() {
throw new RuntimeException();
}
double lower;
double upper;
double n;
}