log1pexp.js (2532B)
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 * ## Notice 20 * 21 * The following copyright and license were part of the original implementation available as part of the [StatsFuns.jl]{@link https://github.com/JuliaStats/StatsFuns.jl/blob/master/src/basicfuns.jl} Julia package. The implementation follows the original, but has been modified for JavaScript. 22 * 23 * ```text 24 * Copyright (c) 2015: Dahua Lin. 25 * 26 * Permission is hereby granted, free of charge, to any person obtaining 27 * a copy of this software and associated documentation files (the 28 * "Software"), to deal in the Software without restriction, including 29 * without limitation the rights to use, copy, modify, merge, publish, 30 * distribute, sublicense, and/or sell copies of the Software, and to 31 * permit persons to whom the Software is furnished to do so, subject to 32 * the following conditions: 33 * 34 * The above copyright notice and this permission notice shall be 35 * included in all copies or substantial portions of the Software. 36 * 37 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, 38 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF 39 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. 40 * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY 41 * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, 42 * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE 43 * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. 44 * ``` 45 */ 46 47 'use strict'; 48 49 // MODULES // 50 51 var log1p = require( '@stdlib/math/base/special/log1p' ); 52 var exp = require( '@stdlib/math/base/special/exp' ); 53 54 55 // MAIN // 56 57 /** 58 * Compute ln( 1 + exp(x) ) without overflow. 59 * 60 * @private 61 * @param {number} x - input value 62 * @returns {number} function value 63 */ 64 function log1pexp( x ) { 65 if ( x <= 18.0 ) { 66 return log1p( exp(x) ); 67 } 68 if ( x > 33.3 ) { 69 return x; 70 } 71 // Case: 18.0 < x <= 33.3 72 return x + exp( -x ); 73 } 74 75 76 // EXPORTS // 77 78 module.exports = log1pexp;