Press n or j to go to the next uncovered block, b, p or k for the previous block.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 | 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 500x 500x 500x 500x 500x 500x 500x 500x 500x 500x 500x 500x 500x 500x 22004x 22004x 22004x 22004x 500x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 504x 504x 504x 504x 3x 3x 504x 1x 1x 500x 500x 500x 500x 504x 1x 1x 1x 1x 1x | /**
* @license Apache-2.0
*
* Copyright (c) 2018 The Stdlib Authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
'use strict';
// MODULES //
var sumSeries = require( '@stdlib/math/base/tools/sum-series' );
var isnan = require( '@stdlib/math/base/assert/is-nan' );
var factorialln = require( '@stdlib/math/base/special/factorialln' );
var factorial = require( '@stdlib/math/base/special/factorial' );
var exp = require( '@stdlib/math/base/special/exp' );
var ln = require( '@stdlib/math/base/special/ln' );
// FUNCTIONS //
/**
* Returns a function to retrieve elements of the series \\( \sum_{k=0}^{\infty} \frac{ \lambda^k \log(k!) }{ k! } \\).
*
* @private
* @param {NonNegativeNumber} lambda - mean parameter
* @returns {Function} function to retrieve series elements
*/
function seriesClosure( lambda ) {
var lk;
var k;
k = 1;
lk = lambda;
return seriesElement;
/**
* Returns the current series element.
*
* @private
* @returns {number} series element
*/
function seriesElement() {
k += 1;
lk *= lambda;
return lk * factorialln( k ) / factorial( k );
}
}
// MAIN //
/**
* Returns the entropy of a Poisson distribution.
*
* @param {NonNegativeNumber} lambda - mean parameter
* @returns {PositiveNumber} entropy
*
* @example
* var v = entropy( 9.0 );
* // returns ~2.508
*
* @example
* var v = entropy( 1.0 );
* // returns ~1.305
*
* @example
* var v = entropy( -0.2 );
* // returns NaN
*
* @example
* var v = entropy( NaN );
* // returns NaN
*/
function entropy( lambda ) {
var gen;
var out;
if ( isnan( lambda ) || lambda < 0.0 ) {
return NaN;
}
if ( lambda === 0.0 ) {
return 0.0;
}
gen = seriesClosure( lambda );
out = lambda * ( 1.0-ln(lambda) );
out += exp( -lambda ) * sumSeries( gen );
return out;
}
// EXPORTS //
module.exports = entropy;
|