upper_gamma_fraction.js (1910B)
1 /** 2 * @license Apache-2.0 3 * 4 * Copyright (c) 2018 The Stdlib Authors. 5 * 6 * Licensed under the Apache License, Version 2.0 (the "License"); 7 * you may not use this file except in compliance with the License. 8 * You may obtain a copy of the License at 9 * 10 * http://www.apache.org/licenses/LICENSE-2.0 11 * 12 * Unless required by applicable law or agreed to in writing, software 13 * distributed under the License is distributed on an "AS IS" BASIS, 14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 15 * See the License for the specific language governing permissions and 16 * limitations under the License. 17 * 18 * 19 * ## Notice 20 * 21 * The original C++ code and copyright notice are from the [Boost library]{@link http://www.boost.org/doc/libs/1_61_0/boost/math/special_functions/gamma.hpp}. The implementation has been modified for JavaScript. 22 * 23 * ```text 24 * Copyright John Maddock 2006-7, 2013-14. 25 * Copyright Paul A. Bristow 2007, 2013-14. 26 * Copyright Nikhar Agrawal 2013-14. 27 * Copyright Christopher Kormanyos 2013-14. 28 * 29 * Use, modification and distribution are subject to the 30 * Boost Software License, Version 1.0. (See accompanying file 31 * LICENSE or copy at http://www.boost.org/LICENSE_1_0.txt) 32 * ``` 33 */ 34 35 'use strict'; 36 37 // MODULES // 38 39 var continuedFraction = require( './../../../../base/tools/continued-fraction' ); 40 var upperIncompleteGammaFract = require( './upper_incomplete_gamma_fract.js' ); 41 42 43 // VARIABLES // 44 45 var OPTS = { 46 'maxIter': 1000 47 }; 48 49 50 // MAIN // 51 52 /** 53 * Evaluate the lower incomplete gamma integral via a series expansion and divide by gamma(z) to normalize. 54 * 55 * @private 56 * @param {number} a - function parameter 57 * @param {number} z - function parameter 58 * @returns {number} function value 59 */ 60 function upperGammaFraction( a, z ) { 61 var f = upperIncompleteGammaFract( a, z ); 62 return 1.0 / ( z - a + 1.0 + continuedFraction( f, OPTS ) ); 63 } 64 65 66 // EXPORTS // 67 68 module.exports = upperGammaFraction;