| /* |
| * 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.ContinuousUniformSampler; |
| |
| /** |
| * Implementation of the <a href="http://en.wikipedia.org/wiki/Uniform_distribution_(continuous)">uniform distribution</a>. |
| */ |
| public class UniformContinuousDistribution extends AbstractContinuousDistribution { |
| /** Lower bound of this distribution (inclusive). */ |
| private final double lower; |
| /** Upper bound of this distribution (exclusive). */ |
| private final double upper; |
| |
| /** |
| * Creates a uniform distribution. |
| * |
| * @param lower Lower bound of this distribution (inclusive). |
| * @param upper Upper bound of this distribution (exclusive). |
| * @throws IllegalArgumentException if {@code lower >= upper}. |
| */ |
| public UniformContinuousDistribution(double lower, |
| double upper) { |
| if (lower >= upper) { |
| throw new DistributionException(DistributionException.INVALID_RANGE_LOW_GTE_HIGH, |
| lower, upper); |
| } |
| |
| this.lower = lower; |
| this.upper = upper; |
| } |
| |
| /** {@inheritDoc} */ |
| @Override |
| public double density(double x) { |
| if (x < lower || |
| x > upper) { |
| return 0; |
| } |
| return 1 / (upper - lower); |
| } |
| |
| /** {@inheritDoc} */ |
| @Override |
| public double cumulativeProbability(double x) { |
| if (x <= lower) { |
| return 0; |
| } |
| if (x >= upper) { |
| return 1; |
| } |
| return (x - lower) / (upper - lower); |
| } |
| |
| /** {@inheritDoc} */ |
| @Override |
| public double inverseCumulativeProbability(final double p) { |
| if (p < 0 || |
| p > 1) { |
| throw new DistributionException(DistributionException.INVALID_PROBABILITY, p); |
| } |
| return p * (upper - lower) + lower; |
| } |
| |
| /** |
| * {@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 * (lower + upper); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * |
| * For lower bound {@code lower} and upper bound {@code upper}, the |
| * variance is {@code (upper - lower)^2 / 12}. |
| */ |
| @Override |
| public double getVariance() { |
| final double ul = upper - lower; |
| return ul * ul / 12; |
| } |
| |
| /** |
| * {@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 double 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 double getSupportUpperBound() { |
| return upper; |
| } |
| |
| /** |
| * {@inheritDoc} |
| * |
| * The support of this distribution is connected. |
| * |
| * @return {@code true} |
| */ |
| @Override |
| public boolean isSupportConnected() { |
| return true; |
| } |
| |
| /** {@inheritDoc} */ |
| @Override |
| public ContinuousDistribution.Sampler createSampler(final UniformRandomProvider rng) { |
| // Uniform distribution sampler. |
| return new ContinuousUniformSampler(rng, lower, upper)::sample; |
| } |
| } |