factory.js (1808B)
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 isnan = require( '@stdlib/math/base/assert/is-nan' ); 25 var mgf0 = require( './_mgf.js' ); 26 27 28 // MAIN // 29 30 /** 31 * Returns a function for evaluating the moment-generating function (MGF) 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} MGF 36 * 37 * @example 38 * var mgf = factory( 0.5, 0.5 ); 39 * 40 * var y = mgf( 0.8 ); 41 * // returns ~1.552 42 * 43 * y = mgf( 0.3 ); 44 * // returns ~1.168 45 */ 46 function factory( alpha, beta ) { 47 if ( 48 isnan( alpha ) || 49 isnan( beta ) || 50 alpha <= 0.0 || 51 beta <= 0.0 52 ) { 53 return constantFunction( NaN ); 54 } 55 return mgf; 56 57 /** 58 * Evaluates the moment-generating function (MGF) for a beta distribution. 59 * 60 * @private 61 * @param {number} t - input value 62 * @returns {number} evaluated MGF 63 * 64 * @example 65 * var y = mgf( 2.0 ); 66 * // returns <number> 67 */ 68 function mgf( t ) { 69 if ( isnan( t ) ) { 70 return NaN; 71 } 72 return mgf0( t, alpha, beta ); 73 } 74 } 75 76 77 // EXPORTS // 78 79 module.exports = factory;