factory.js (1999B)
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 ldfrechet = require( './../../../../../base/dists/frechet/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 Fréchet distribution with shape `alpha`, scale `s`, and location `m`. 33 * 34 * @param {PositiveNumber} alpha - shape parameter 35 * @param {PositiveNumber} s - scale parameter 36 * @param {number} m - location parameter 37 * @returns {Function} PDF 38 * 39 * @example 40 * var pdf = factory( 3.0, 3.0, 5.0 ); 41 * 42 * var y = pdf( 10.0 ); 43 * // returns ~0.104 44 * 45 * y = pdf( 7.0 ); 46 * // returns ~0.173 47 */ 48 function factory( alpha, s, m ) { 49 var logpdf; 50 if ( 51 isnan( alpha ) || 52 isnan( s ) || 53 isnan( m ) || 54 alpha <= 0.0 || 55 s <= 0.0 56 ) { 57 return constantFunction( NaN ); 58 } 59 logpdf = ldfrechet( alpha, s, m ); 60 return pdf; 61 62 /** 63 * Evaluates the probability density function (PDF) for a Fréchet distribution. 64 * 65 * @private 66 * @param {number} x - input value 67 * @returns {number} evaluated PDF 68 * 69 * @example 70 * var y = pdf( -2.0 ); 71 * // returns <number> 72 */ 73 function pdf( x ) { 74 if ( isnan( x ) ) { 75 return NaN; 76 } 77 return exp( logpdf( x, alpha, s, m ) ); 78 } 79 } 80 81 82 // EXPORTS // 83 84 module.exports = factory;