108 lines
2.7 KiB
JavaScript
108 lines
2.7 KiB
JavaScript
/**
|
|
* @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 isPositiveInteger = require( '@stdlib/assert/is-positive-integer' ).isPrimitive;
|
|
var incrmmean = require( './../../../incr/mmean' );
|
|
|
|
|
|
// MAIN //
|
|
|
|
/**
|
|
* Returns an accumulator function which incrementally computes a moving harmonic mean.
|
|
*
|
|
* ## Method
|
|
*
|
|
* - The harmonic mean of positive real numbers \\(x_0, x_1, \ldots, x_{n-1}\\) is defined as
|
|
*
|
|
* ```tex
|
|
* \begin{align*}
|
|
* H &= \frac{n}{\frac{1}{x_0} + \frac{1}{x_1} + \cdots + \frac{1}{x_{n-1}}} \\
|
|
* &= \frac{n}{\sum_{i=0}^{n-1} \frac{1}{x_i}}
|
|
* \end{align*}
|
|
* ```
|
|
*
|
|
* which may be expressed
|
|
*
|
|
* ```tex
|
|
* H = \biggl( \frac{\sum_{i=0}^{n-1} \frac{1}{x_i}}{n} \biggr)^{-1}
|
|
* ```
|
|
*
|
|
* - 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.
|
|
*
|
|
* @param {PositiveInteger} W - window size
|
|
* @throws {TypeError} must provide a positive integer
|
|
* @returns {Function} accumulator function
|
|
*
|
|
* @example
|
|
* var accumulator = incrmhmean( 3 );
|
|
*
|
|
* var v = accumulator();
|
|
* // returns null
|
|
*
|
|
* v = accumulator( 2.0 );
|
|
* // returns 2.0
|
|
*
|
|
* v = accumulator( 5.0 );
|
|
* // returns ~2.86
|
|
*
|
|
* v = accumulator( 3.0 );
|
|
* // returns ~2.90
|
|
*
|
|
* v = accumulator( 5.0 );
|
|
* // returns ~4.09
|
|
*
|
|
* v = accumulator();
|
|
* // returns ~4.09
|
|
*/
|
|
function incrmhmean( W ) {
|
|
var mmean;
|
|
if ( !isPositiveInteger( W ) ) {
|
|
throw new TypeError( 'invalid argument. Must provide a positive integer. Value: `' + W + '`.' );
|
|
}
|
|
mmean = incrmmean( W );
|
|
return accumulator;
|
|
|
|
/**
|
|
* 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.
|
|
*
|
|
* @private
|
|
* @param {number} [x] - input value
|
|
* @returns {(number|null)} harmonic mean or null
|
|
*/
|
|
function accumulator( x ) {
|
|
var v;
|
|
if ( arguments.length === 0 ) {
|
|
v = mmean();
|
|
if ( v === null ) {
|
|
return v;
|
|
}
|
|
return 1.0 / v;
|
|
}
|
|
return 1.0 / mmean( 1.0/x );
|
|
}
|
|
}
|
|
|
|
|
|
// EXPORTS //
|
|
|
|
module.exports = incrmhmean;
|