time-to-botec

Benchmark sampling in different programming languages
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entropy.js (1943B)

      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 isNonNegativeInteger = require( '@stdlib/math/base/assert/is-nonnegative-integer' );
     24 var isnan = require( '@stdlib/math/base/assert/is-nan' );
     25 var exp = require( '@stdlib/math/base/special/exp' );
     26 var ln = require( '@stdlib/math/base/special/ln' );
     27 var PINF = require( '@stdlib/constants/float64/pinf' );
     28 
     29 
     30 // MAIN //
     31 
     32 /**
     33 * Returns the entropy of a binomial distribution.
     34 *
     35 * @param {NonNegativeInteger} n - number of trials
     36 * @param {Probability} p - success probability
     37 * @returns {number} entropy
     38 *
     39 * @example
     40 * var v = entropy( 100, 0.1 );
     41 * // returns ~2.511
     42 *
     43 * @example
     44 * var v = entropy( 20, 0.5 );
     45 * // returns ~2.223
     46 *
     47 * @example
     48 * var v = entropy( 10.3, 0.5 );
     49 * // returns NaN
     50 *
     51 * @example
     52 * var v = entropy( 20, 1.1 );
     53 * // returns NaN
     54 *
     55 * @example
     56 * var v = entropy( 20, NaN );
     57 * // returns NaN
     58 */
     59 function entropy( n, p ) {
     60 	var nlq;
     61 	var out;
     62 	var i;
     63 	var q;
     64 
     65 	if (
     66 		isnan( n ) ||
     67 		isnan( p ) ||
     68 		p < 0.0 ||
     69 		p > 1.0 ||
     70 		!isNonNegativeInteger( n ) ||
     71 		n === PINF
     72 	) {
     73 		return NaN;
     74 	}
     75 	if ( p === 0 || p === 1 || n === 0 ) {
     76 		return 0.0;
     77 	}
     78 	q = 1.0 - p;
     79 	nlq = n * ln( q );
     80 	out = exp( nlq ) * nlq;
     81 	for ( i = 1; i <= n; i++ ) {
     82 		nlq += ln( ( n - i + 1 ) / i ) + ln( p / q );
     83 		out += exp( nlq ) * nlq;
     84 	}
     85 	return -out;
     86 }
     87 
     88 
     89 // EXPORTS //
     90 
     91 module.exports = entropy;