factory.js (1977B)
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/logcdf' ).factory; 25 var isnan = require( '@stdlib/math/base/assert/is-nan' ); 26 var log1pexp = require( './log1pexp.js' ); 27 28 29 // MAIN // 30 31 /** 32 * Returns a function for evaluating the logarithm of the cumulative distribution function (CDF) for a logistic distribution with location parameter `mu` and scale parameter `s`. 33 * 34 * @param {number} mu - location parameter 35 * @param {NonNegativeNumber} s - scale parameter 36 * @returns {Function} logCDF 37 * 38 * @example 39 * var logcdf = factory( 3.0, 1.5 ); 40 * 41 * var y = logcdf( 1.0 ); 42 * // returns ~-1.567 43 * 44 * y = logcdf( 4.0 ); 45 * // returns ~-0.414 46 */ 47 function factory( mu, s ) { 48 if ( isnan( mu ) || isnan( s ) || s < 0.0 ) { 49 return constantFunction( NaN ); 50 } 51 if ( s === 0.0 ) { 52 return degenerate( mu ); 53 } 54 return logcdf; 55 56 /** 57 * Evaluates the logarithm of the cumulative distribution function (CDF) for a logistic distribution. 58 * 59 * @private 60 * @param {number} x - input value 61 * @returns {number} evaluated logCDF 62 * 63 * @example 64 * var y = logcdf( 2.0 ); 65 * // returns <number> 66 */ 67 function logcdf( x ) { 68 var z; 69 if ( isnan( x ) ) { 70 return NaN; 71 } 72 z = ( x - mu ) / s; 73 return -log1pexp( -z ); 74 } 75 } 76 77 78 // EXPORTS // 79 80 module.exports = factory;