factory.js (1979B)
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 logpdfFactory = require( './../../../../../base/dists/betaprime/logpdf' ).factory; 25 var isnan = require( '@stdlib/math/base/assert/is-nan' ); 26 var exp = require( '@stdlib/math/base/special/exp' ); 27 28 29 // MAIN // 30 31 /** 32 * Returns a function for evaluating the probability density function (PDF) for a beta prime distribution with first shape parameter `alpha` and second shape parameter `beta`. 33 * 34 * @param {PositiveNumber} alpha - first shape parameter 35 * @param {PositiveNumber} beta - second shape parameter 36 * @returns {Function} PDF 37 * 38 * @example 39 * var pdf = factory( 0.5, 0.5 ); 40 * 41 * var y = pdf( 0.8 ); 42 * // returns ~0.198 43 * 44 * y = pdf( 0.3 ); 45 * // returns ~0.447 46 */ 47 function factory( alpha, beta ) { 48 var logpdf; 49 if ( 50 isnan( alpha ) || 51 isnan( beta ) || 52 alpha <= 0.0 || 53 beta <= 0.0 54 ) { 55 return constantFunction( NaN ); 56 } 57 logpdf = logpdfFactory( alpha, beta ); 58 return pdf; 59 60 /** 61 * Evaluates the probability density function (PDF) for a beta prime distribution. 62 * 63 * @private 64 * @param {number} x - input value 65 * @returns {number} evaluated PDF 66 * 67 * @example 68 * var y = pdf( 0.3 ); 69 * // returns <number> 70 */ 71 function pdf( x ) { 72 if ( isnan( x ) ) { 73 return NaN; 74 } 75 return exp( logpdf( x ) ); 76 } 77 } 78 79 80 // EXPORTS // 81 82 module.exports = factory;