time-to-botec

Benchmark sampling in different programming languages
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main.js (2724B)

      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 isPositiveInteger = require( '@stdlib/assert/is-positive-integer' ).isPrimitive;
     24 var incrmmean = require( './../../../incr/mmean' );
     25 
     26 
     27 // MAIN //
     28 
     29 /**
     30 * Returns an accumulator function which incrementally computes a moving harmonic mean.
     31 *
     32 * ## Method
     33 *
     34 * -   The harmonic mean of positive real numbers \\(x_0, x_1, \ldots, x_{n-1}\\) is defined as
     35 *
     36 *     ```tex
     37 *     \begin{align*}
     38 *     H &= \frac{n}{\frac{1}{x_0} + \frac{1}{x_1} + \cdots + \frac{1}{x_{n-1}}} \\
     39 *       &= \frac{n}{\sum_{i=0}^{n-1} \frac{1}{x_i}}
     40 *     \end{align*}
     41 *     ```
     42 *
     43 *     which may be expressed
     44 *
     45 *     ```tex
     46 *     H = \biggl( \frac{\sum_{i=0}^{n-1} \frac{1}{x_i}}{n} \biggr)^{-1}
     47 *     ```
     48 *
     49 * -   Accordingly, to compute the harmonic mean for each window incrementally, we can simply compute the arithmetic mean of reciprocal values and then compute the reciprocal of the result.
     50 *
     51 * @param {PositiveInteger} W - window size
     52 * @throws {TypeError} must provide a positive integer
     53 * @returns {Function} accumulator function
     54 *
     55 * @example
     56 * var accumulator = incrmhmean( 3 );
     57 *
     58 * var v = accumulator();
     59 * // returns null
     60 *
     61 * v = accumulator( 2.0 );
     62 * // returns 2.0
     63 *
     64 * v = accumulator( 5.0 );
     65 * // returns ~2.86
     66 *
     67 * v = accumulator( 3.0 );
     68 * // returns ~2.90
     69 *
     70 * v = accumulator( 5.0 );
     71 * // returns ~4.09
     72 *
     73 * v = accumulator();
     74 * // returns ~4.09
     75 */
     76 function incrmhmean( W ) {
     77 	var mmean;
     78 	if ( !isPositiveInteger( W ) ) {
     79 		throw new TypeError( 'invalid argument. Must provide a positive integer. Value: `' + W + '`.' );
     80 	}
     81 	mmean = incrmmean( W );
     82 	return accumulator;
     83 
     84 	/**
     85 	* If provided a value, the accumulator function returns an updated harmonic mean. If not provided a value, the accumulator function returns the current harmonic mean.
     86 	*
     87 	* @private
     88 	* @param {number} [x] - input value
     89 	* @returns {(number|null)} harmonic mean or null
     90 	*/
     91 	function accumulator( x ) {
     92 		var v;
     93 		if ( arguments.length === 0 ) {
     94 			v = mmean();
     95 			if ( v === null ) {
     96 				return v;
     97 			}
     98 			return 1.0 / v;
     99 		}
    100 		return 1.0 / mmean( 1.0/x );
    101 	}
    102 }
    103 
    104 
    105 // EXPORTS //
    106 
    107 module.exports = incrmhmean;