factory.js (1911B)
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 constantFunction = require( '@stdlib/utils/constant-function' ); 24 var betaincinv = require( '@stdlib/math/base/special/betaincinv' ); 25 var isnan = require( '@stdlib/math/base/assert/is-nan' ); 26 27 28 // MAIN // 29 30 /** 31 * Returns a function for evaluating the quantile function for a beta distribution with first shape parameter `alpha` and second shape parameter `beta`. 32 * 33 * @param {PositiveNumber} alpha - first shape parameter 34 * @param {PositiveNumber} beta - second shape parameter 35 * @returns {Function} quantile function 36 * 37 * @example 38 * var quantile = factory( 2.5, 0.5 ); 39 * var y = quantile( 0.5 ); 40 * // returns ~0.904 41 * 42 * y = quantile( 0.8 ); 43 * // returns ~0.986 44 */ 45 function factory( alpha, beta ) { 46 if ( 47 isnan( alpha ) || 48 isnan( beta ) || 49 alpha <= 0.0 || 50 beta <= 0.0 51 ) { 52 return constantFunction( NaN ); 53 } 54 return quantile; 55 56 /** 57 * Evaluates the quantile function for a beta distribution. 58 * 59 * @private 60 * @param {Probability} p - input value 61 * @returns {number} evaluated quantile function 62 * 63 * @example 64 * var y = quantile( 0.3 ); 65 * // returns <number> 66 */ 67 function quantile( p ) { 68 if ( 69 isnan( p ) || 70 p < 0.0 || 71 p > 1.0 72 ) { 73 return NaN; 74 } 75 return betaincinv( p, alpha, beta ); 76 } 77 } 78 79 80 // EXPORTS // 81 82 module.exports = factory;