main.js (1428B)
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 isnan = require( './../../../../base/assert/is-nan' ); 24 var log1p = require( './../../../../base/special/log1p' ); 25 var exp = require( './../../../../base/special/exp' ); 26 27 28 // MAIN // 29 30 /** 31 * Computes the natural logarithm of \\( 1 + \exp(x) \\). 32 * 33 * @param {number} x - input value 34 * @returns {number} function value 35 * 36 * @example 37 * var v = log1pexp( 1.1 ); 38 * // returns ~1.387 39 * 40 * @example 41 * var v = log1pexp( 100.0 ); 42 * // returns 100.0 43 * 44 * @example 45 * var v = log1pexp( NaN ); 46 * // returns NaN 47 */ 48 function log1pexp( x ) { 49 if ( isnan( x ) ) { 50 return NaN; 51 } 52 if ( x <= -37.0 ) { 53 return exp( x ); 54 } 55 if ( x <= 18.0 ) { 56 return log1p( exp( x ) ); 57 } 58 if ( x <= 33.3 ) { 59 return x + exp( -x ); 60 } 61 // Case: x > 33.3 62 return x; 63 } 64 65 66 // EXPORTS // 67 68 module.exports = log1pexp;