factory.js (1578B)
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 'use strict'; 20 21 // MODULES // 22 23 var gammaFactory = require( './../../../../../base/dists/gamma/quantile' ).factory; 24 var sqrt = require( '@stdlib/math/base/special/sqrt' ); 25 26 27 // MAIN // 28 29 /** 30 * Returns a function for evaluating the quantile function for a chi distribution with degrees of freedom `k`. 31 * 32 * @param {NonNegativeNumber} k - degrees of freedom 33 * @returns {Function} quantile function 34 * 35 * @example 36 * var quantile = factory( 0.4 ); 37 * 38 * var y = quantile( 0.9 ); 39 * // returns ~1.1 40 * 41 * y = quantile( 1.0 ); 42 * // returns Infinity 43 */ 44 function factory( k ) { 45 var gamma = gammaFactory( k/2.0, 0.5 ); 46 return quantile; 47 48 /** 49 * Evaluates the quantile function for a chi distribution. 50 * 51 * @private 52 * @param {Probability} p - input value 53 * @returns {number} evaluated quantile function 54 * 55 * @example 56 * var y = quantile( 0.3 ); 57 * // returns <number> 58 */ 59 function quantile( p ) { 60 return sqrt( gamma( p ) ); 61 } 62 } 63 64 65 // EXPORTS // 66 67 module.exports = factory;