main.js (1316B)
1 /** 2 * @license Apache-2.0 3 * 4 * Copyright (c) 2019 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 isnan = require( './../../../../base/assert/is-nan' ); 24 var exp = require( './../../../../base/special/exp' ); 25 26 27 // MAIN // 28 29 /** 30 * Evaluates the standard logistic function. 31 * 32 * @param {number} x - input value 33 * @returns {number} function value 34 * 35 * @example 36 * var y = expit( 0.0 ); 37 * // returns 0.5 38 * 39 * @example 40 * var y = expit( 1.0 ); 41 * // returns ~0.731 42 * 43 * @example 44 * var y = expit( -1.0 ); 45 * // returns ~0.269 46 * 47 * @example 48 * var y = expit( Infinity ); 49 * // returns 1.0 50 * 51 * @example 52 * var y = expit( NaN ); 53 * // returns NaN 54 */ 55 function expit( x ) { 56 if ( isnan( x ) ) { 57 return x; 58 } 59 return 1.0 / ( 1.0 + exp( -x ) ); 60 } 61 62 63 // EXPORTS // 64 65 module.exports = expit;