org.apache.commons.numbers.gamma.LogGamma1p Maven / Gradle / Ivy
/*
* 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.numbers.gamma;
/**
* Function \( \ln \Gamma(1 + x) \).
*
* Class is immutable.
*/
final class LogGamma1p {
/** Private constructor. */
private LogGamma1p() {
// intentionally empty
}
/**
* Computes the function \( \ln \Gamma(1 + x) \) for \( -0.5 \leq x \leq 1.5 \).
*
* This implementation is based on the double precision implementation in
* the NSWC Library of Mathematics Subroutines, {@code DGMLN1}.
*
* @param x Argument.
* @return \( \ln \Gamma(1 + x) \)
* @throws IllegalArgumentException if {@code x < -0.5} or {@code x > 1.5}.
*/
public static double value(final double x) {
if (x < -0.5 || x > 1.5) {
throw new GammaException(GammaException.OUT_OF_RANGE, x, -0.5, 1.5);
}
return -Math.log1p(InvGamma1pm1.value(x));
}
}