factory.js (2002B)
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 degenerate = require( './../../../../../base/dists/degenerate/mgf' ).factory; 25 var isnan = require( '@stdlib/math/base/assert/is-nan' ); 26 var sinc = require( '@stdlib/math/base/special/sinc' ); 27 var exp = require( '@stdlib/math/base/special/exp' ); 28 var abs = require( '@stdlib/math/base/special/abs' ); 29 30 31 // MAIN // 32 33 /** 34 * Returns a function for evaluating the moment-generating function (MGF) of a logistic distribution with mean `mu` and scale parameter `s`. 35 * 36 * @param {number} mu - mean 37 * @param {NonNegativeNumber} s - scale parameter 38 * @returns {Function} MGF 39 * 40 * @example 41 * var mgf = factory( 10.0, 0.5 ); 42 * 43 * var y = mgf( 0.5 ); 44 * // returns ~164.846 45 * 46 * y = mgf( 2.0 ); 47 * // returns Infinity 48 */ 49 function factory( mu, s ) { 50 if ( isnan( mu ) || isnan( s ) || s < 0.0 ) { 51 return constantFunction( NaN ); 52 } 53 if ( s === 0.0 ) { 54 return degenerate( mu ); 55 } 56 return mgf; 57 58 /** 59 * Evaluates the moment-generating function (MGF) for a logistic distribution. 60 * 61 * @private 62 * @param {number} t - input value 63 * @returns {number} evaluated MGF 64 * 65 * @example 66 * var y = mgf( 0.5 ); 67 * // returns <number> 68 */ 69 function mgf( t ) { 70 var st = s * t; 71 if ( abs( st ) > 1.0 ) { 72 return NaN; 73 } 74 return exp( mu * t ) / sinc( st ); 75 } 76 } 77 78 79 // EXPORTS // 80 81 module.exports = factory;