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Diffstat (limited to 'src/main/java/org/apache/commons/math3/distribution/LaplaceDistribution.java')
-rw-r--r-- | src/main/java/org/apache/commons/math3/distribution/LaplaceDistribution.java | 160 |
1 files changed, 160 insertions, 0 deletions
diff --git a/src/main/java/org/apache/commons/math3/distribution/LaplaceDistribution.java b/src/main/java/org/apache/commons/math3/distribution/LaplaceDistribution.java new file mode 100644 index 0000000..2ce36fc --- /dev/null +++ b/src/main/java/org/apache/commons/math3/distribution/LaplaceDistribution.java @@ -0,0 +1,160 @@ +/* + * 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.NotStrictlyPositiveException; +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; + +/** + * This class implements the Laplace distribution. + * + * @see <a href="http://en.wikipedia.org/wiki/Laplace_distribution">Laplace distribution + * (Wikipedia)</a> + * @since 3.4 + */ +public class LaplaceDistribution extends AbstractRealDistribution { + + /** Serializable version identifier. */ + private static final long serialVersionUID = 20141003; + + /** The location parameter. */ + private final double mu; + + /** The scale parameter. */ + private final double beta; + + /** + * Build a new instance. + * + * <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 mu location parameter + * @param beta scale parameter (must be positive) + * @throws NotStrictlyPositiveException if {@code beta <= 0} + */ + public LaplaceDistribution(double mu, double beta) { + this(new Well19937c(), mu, beta); + } + + /** + * Build a new instance. + * + * @param rng Random number generator + * @param mu location parameter + * @param beta scale parameter (must be positive) + * @throws NotStrictlyPositiveException if {@code beta <= 0} + */ + public LaplaceDistribution(RandomGenerator rng, double mu, double beta) { + super(rng); + + if (beta <= 0.0) { + throw new NotStrictlyPositiveException(LocalizedFormats.NOT_POSITIVE_SCALE, beta); + } + + this.mu = mu; + this.beta = beta; + } + + /** + * Access the location parameter, {@code mu}. + * + * @return the location parameter. + */ + public double getLocation() { + return mu; + } + + /** + * Access the scale parameter, {@code beta}. + * + * @return the scale parameter. + */ + public double getScale() { + return beta; + } + + /** {@inheritDoc} */ + public double density(double x) { + return FastMath.exp(-FastMath.abs(x - mu) / beta) / (2.0 * beta); + } + + /** {@inheritDoc} */ + public double cumulativeProbability(double x) { + if (x <= mu) { + return FastMath.exp((x - mu) / beta) / 2.0; + } else { + return 1.0 - FastMath.exp((mu - x) / beta) / 2.0; + } + } + + /** {@inheritDoc} */ + @Override + public double inverseCumulativeProbability(double p) throws OutOfRangeException { + if (p < 0.0 || p > 1.0) { + throw new OutOfRangeException(p, 0.0, 1.0); + } else if (p == 0) { + return Double.NEGATIVE_INFINITY; + } else if (p == 1) { + return Double.POSITIVE_INFINITY; + } + double x = (p > 0.5) ? -Math.log(2.0 - 2.0 * p) : Math.log(2.0 * p); + return mu + beta * x; + } + + /** {@inheritDoc} */ + public double getNumericalMean() { + return mu; + } + + /** {@inheritDoc} */ + public double getNumericalVariance() { + return 2.0 * beta * beta; + } + + /** {@inheritDoc} */ + public double getSupportLowerBound() { + return Double.NEGATIVE_INFINITY; + } + + /** {@inheritDoc} */ + public double getSupportUpperBound() { + return Double.POSITIVE_INFINITY; + } + + /** {@inheritDoc} */ + public boolean isSupportLowerBoundInclusive() { + return false; + } + + /** {@inheritDoc} */ + public boolean isSupportUpperBoundInclusive() { + return false; + } + + /** {@inheritDoc} */ + public boolean isSupportConnected() { + return true; + } +} |