| /* |
| * 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.statistics.distribution; |
| |
| import org.apache.commons.rng.UniformRandomProvider; |
| import org.apache.commons.rng.sampling.distribution.DiscreteUniformSampler; |
| |
| /** |
| * Implementation of the <a href="http://en.wikipedia.org/wiki/Uniform_distribution_(discrete)"> |
| * uniform integer distribution</a>. |
| */ |
| public class UniformDiscreteDistribution extends AbstractDiscreteDistribution { |
| /** 1 / 12. **/ |
| private static final double ONE_TWELFTH = 1 / 12d; |
| /** Lower bound (inclusive) of this distribution. */ |
| private final int lower; |
| /** Upper bound (inclusive) of this distribution. */ |
| private final int upper; |
| /** "upper" + "lower" (to avoid overflow). */ |
| private final double upperPlusLower; |
| /** "upper" - "lower" (to avoid overflow). */ |
| private final double upperMinusLower; |
| |
| /** |
| * Creates a new uniform integer distribution using the given lower and |
| * upper bounds (both inclusive). |
| * |
| * @param lower Lower bound (inclusive) of this distribution. |
| * @param upper Upper bound (inclusive) of this distribution. |
| * @throws IllegalArgumentException if {@code lower > upper}. |
| */ |
| public UniformDiscreteDistribution(int lower, |
| int upper) { |
| if (lower > upper) { |
| throw new DistributionException(DistributionException.INVALID_RANGE_LOW_GT_HIGH, |
| lower, upper); |
| } |
| this.lower = lower; |
| this.upper = upper; |
| upperPlusLower = (double) upper + (double) lower; |
| upperMinusLower = (double) upper - (double) lower; |
| } |
| |
| /** {@inheritDoc} */ |
| @Override |
| public double probability(int x) { |
| if (x < lower || x > upper) { |
| return 0; |
| } |
| return 1 / (upperMinusLower + 1); |
| } |
| |
| /** {@inheritDoc} */ |
| @Override |
| public double cumulativeProbability(int x) { |
| if (x < lower) { |
| return 0; |
| } |
| if (x > upper) { |
| return 1; |
| } |
| return (x - lower + 1) / (upperMinusLower + 1); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * |
| * For lower bound {@code lower} and upper bound {@code upper}, the mean is |
| * {@code 0.5 * (lower + upper)}. |
| */ |
| @Override |
| public double getMean() { |
| return 0.5 * upperPlusLower; |
| } |
| |
| /** |
| * {@inheritDoc} |
| * |
| * For lower bound {@code lower} and upper bound {@code upper}, and |
| * {@code n = upper - lower + 1}, the variance is {@code (n^2 - 1) / 12}. |
| */ |
| @Override |
| public double getVariance() { |
| final double n = upperMinusLower + 1; |
| return ONE_TWELFTH * (n * n - 1); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * |
| * The lower bound of the support is equal to the lower bound parameter |
| * of the distribution. |
| * |
| * @return lower bound of the support |
| */ |
| @Override |
| public int getSupportLowerBound() { |
| return lower; |
| } |
| |
| /** |
| * {@inheritDoc} |
| * |
| * The upper bound of the support is equal to the upper bound parameter |
| * of the distribution. |
| * |
| * @return upper bound of the support |
| */ |
| @Override |
| public int getSupportUpperBound() { |
| return upper; |
| } |
| |
| /** |
| * {@inheritDoc} |
| * |
| * The support of this distribution is connected. |
| * |
| * @return {@code true} |
| */ |
| @Override |
| public boolean isSupportConnected() { |
| return true; |
| } |
| |
| /**{@inheritDoc} */ |
| @Override |
| public DiscreteDistribution.Sampler createSampler(final UniformRandomProvider rng) { |
| // Discrete uniform distribution sampler. |
| return new DiscreteUniformSampler(rng, lower, upper)::sample; |
| } |
| } |