main.js (1580B)
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 exp = require( './../../../../base/special/exp' ); 25 var log1p = require( './../../../../base/special/log1p' ); 26 var LN2 = require( '@stdlib/constants/float64/ln-two' ); 27 28 29 // MAIN // 30 31 /** 32 * Computes the natural logarithm of \\( \exp(x) + \exp(y) \\). 33 * 34 * @param {number} x - input value 35 * @param {number} y - input value 36 * @returns {number} natural logarithm of \\( \exp(x) + \exp(y) \\) 37 * 38 * @example 39 * var v = logaddexp( 90.0, 90.0 ); 40 * // returns ~90.6931 41 * 42 * @example 43 * var v = logaddexp( -20.0, 90.0 ); 44 * // returns 90.0 45 * 46 * @example 47 * var v = logaddexp( 0.0, -100 ); 48 * // returns ~3.7201e-44 49 */ 50 function logaddexp( x, y ) { 51 var d; 52 if ( isnan( x ) || isnan( y ) ) { 53 return NaN; 54 } 55 if ( x === y ) { 56 return x + LN2; 57 } 58 d = x - y; 59 if ( d > 0.0 ) { 60 return x + log1p( exp( -d ) ); 61 } 62 return y + log1p( exp( d ) ); 63 } 64 65 66 // EXPORTS // 67 68 module.exports = logaddexp;