entropy.js (1456B)
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( '@stdlib/math/base/assert/is-nan' ); 24 var ln = require( '@stdlib/math/base/special/ln' ); 25 26 27 // MAIN // 28 29 /** 30 * Returns the entropy of a Bernoulli distribution. 31 * 32 * @param {Probability} p - success probability 33 * @returns {PositiveNumber} entropy 34 * 35 * @example 36 * var v = entropy( 0.1 ); 37 * // returns ~0.325 38 * 39 * @example 40 * var v = entropy( 0.5 ); 41 * // returns ~0.693 42 * 43 * @example 44 * var v = entropy( 0.9 ); 45 * // returns ~0.325 46 * 47 * @example 48 * var v = entropy( 1.1 ); 49 * // returns NaN 50 * 51 * @example 52 * var v = entropy( NaN ); 53 * // returns NaN 54 */ 55 function entropy( p ) { 56 var q; 57 if ( 58 isnan( p ) || 59 p < 0.0 || 60 p > 1.0 61 ) { 62 return NaN; 63 } 64 if ( p === 0.0 || p === 1.0 ) { 65 return 0.0; 66 } 67 q = 1.0 - p; 68 return ( -q * ln( q ) ) - ( p * ln( p ) ); 69 } 70 71 72 // EXPORTS // 73 74 module.exports = entropy;