| /* |
| * 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.math3.distribution; |
| |
| import org.apache.commons.math3.exception.OutOfRangeException; |
| import org.apache.commons.math3.exception.util.LocalizedFormats; |
| import org.apache.commons.math3.random.RandomGenerator; |
| import org.apache.commons.math3.random.Well19937c; |
| import org.apache.commons.math3.util.FastMath; |
| |
| /** |
| * Implementation of the geometric distribution. |
| * |
| * @see <a href="http://en.wikipedia.org/wiki/Geometric_distribution">Geometric distribution (Wikipedia)</a> |
| * @see <a href="http://mathworld.wolfram.com/GeometricDistribution.html">Geometric Distribution (MathWorld)</a> |
| * @since 3.3 |
| */ |
| public class GeometricDistribution extends AbstractIntegerDistribution { |
| |
| /** Serializable version identifier. */ |
| private static final long serialVersionUID = 20130507L; |
| /** The probability of success. */ |
| private final double probabilityOfSuccess; |
| /** {@code log(p)} where p is the probability of success. */ |
| private final double logProbabilityOfSuccess; |
| /** {@code log(1 - p)} where p is the probability of success. */ |
| private final double log1mProbabilityOfSuccess; |
| |
| /** |
| * Create a geometric distribution with the given probability of success. |
| * <p> |
| * <b>Note:</b> this constructor will implicitly create an instance of |
| * {@link Well19937c} as random generator to be used for sampling only (see |
| * {@link #sample()} and {@link #sample(int)}). In case no sampling is |
| * needed for the created distribution, it is advised to pass {@code null} |
| * as random generator via the appropriate constructors to avoid the |
| * additional initialisation overhead. |
| * |
| * @param p probability of success. |
| * @throws OutOfRangeException if {@code p <= 0} or {@code p > 1}. |
| */ |
| public GeometricDistribution(double p) { |
| this(new Well19937c(), p); |
| } |
| |
| /** |
| * Creates a geometric distribution. |
| * |
| * @param rng Random number generator. |
| * @param p Probability of success. |
| * @throws OutOfRangeException if {@code p <= 0} or {@code p > 1}. |
| */ |
| public GeometricDistribution(RandomGenerator rng, double p) { |
| super(rng); |
| |
| if (p <= 0 || p > 1) { |
| throw new OutOfRangeException(LocalizedFormats.OUT_OF_RANGE_LEFT, p, 0, 1); |
| } |
| |
| probabilityOfSuccess = p; |
| logProbabilityOfSuccess = FastMath.log(p); |
| log1mProbabilityOfSuccess = FastMath.log1p(-p); |
| } |
| |
| /** |
| * Access the probability of success for this distribution. |
| * |
| * @return the probability of success. |
| */ |
| public double getProbabilityOfSuccess() { |
| return probabilityOfSuccess; |
| } |
| |
| /** {@inheritDoc} */ |
| public double probability(int x) { |
| if (x < 0) { |
| return 0.0; |
| } else { |
| return FastMath.exp(log1mProbabilityOfSuccess * x) * probabilityOfSuccess; |
| } |
| } |
| |
| /** {@inheritDoc} */ |
| @Override |
| public double logProbability(int x) { |
| if (x < 0) { |
| return Double.NEGATIVE_INFINITY; |
| } else { |
| return x * log1mProbabilityOfSuccess + logProbabilityOfSuccess; |
| } |
| } |
| |
| /** {@inheritDoc} */ |
| public double cumulativeProbability(int x) { |
| if (x < 0) { |
| return 0.0; |
| } else { |
| return -FastMath.expm1(log1mProbabilityOfSuccess * (x + 1)); |
| } |
| } |
| |
| /** |
| * {@inheritDoc} |
| * |
| * For probability parameter {@code p}, the mean is {@code (1 - p) / p}. |
| */ |
| public double getNumericalMean() { |
| return (1 - probabilityOfSuccess) / probabilityOfSuccess; |
| } |
| |
| /** |
| * {@inheritDoc} |
| * |
| * For probability parameter {@code p}, the variance is |
| * {@code (1 - p) / (p * p)}. |
| */ |
| public double getNumericalVariance() { |
| return (1 - probabilityOfSuccess) / (probabilityOfSuccess * probabilityOfSuccess); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * |
| * The lower bound of the support is always 0. |
| * |
| * @return lower bound of the support (always 0) |
| */ |
| public int getSupportLowerBound() { |
| return 0; |
| } |
| |
| /** |
| * {@inheritDoc} |
| * |
| * The upper bound of the support is infinite (which we approximate as |
| * {@code Integer.MAX_VALUE}). |
| * |
| * @return upper bound of the support (always Integer.MAX_VALUE) |
| */ |
| public int getSupportUpperBound() { |
| return Integer.MAX_VALUE; |
| } |
| |
| /** |
| * {@inheritDoc} |
| * |
| * The support of this distribution is connected. |
| * |
| * @return {@code true} |
| */ |
| public boolean isSupportConnected() { |
| return true; |
| } |
| |
| /** |
| * {@inheritDoc} |
| */ |
| @Override |
| public int inverseCumulativeProbability(double p) throws OutOfRangeException { |
| if (p < 0 || p > 1) { |
| throw new OutOfRangeException(p, 0, 1); |
| } |
| if (p == 1) { |
| return Integer.MAX_VALUE; |
| } |
| if (p == 0) { |
| return 0; |
| } |
| return Math.max(0, (int) Math.ceil(FastMath.log1p(-p)/log1mProbabilityOfSuccess-1)); |
| } |
| } |