time-to-botec/js/node_modules/@stdlib/stats/incr/hmean/README.md

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@license Apache-2.0
Copyright (c) 2018 The Stdlib Authors.
Licensed under the Apache License, Version 2.0 (the "License");
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# incrhmean
> Compute a [harmonic mean][harmonic-mean] incrementally.
<section class="intro">
The [harmonic mean][harmonic-mean] of positive real numbers `x_0, x_1, ..., x_{n-1}` is defined as
<!-- <equation class="equation" label="eq:harmonic_mean" align="center" raw="\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}} \\ &= \biggl( \frac{\sum_{i=0}^{n-1} \frac{1}{x_i}}{n} \biggr)^{-1}\end{align}" alt="Equation for the harmonic mean."> -->
<div class="equation" align="center" data-raw-text="\begin{align}H &amp;= \frac{n}{\frac{1}{x_0} + \frac{1}{x_1} + \cdots + \frac{1}{x_{n-1}}} \\ &amp;= \frac{n}{\sum_{i=0}^{n-1} \frac{1}{x_i}} \\ &amp;= \biggl( \frac{\sum_{i=0}^{n-1} \frac{1}{x_i}}{n} \biggr)^{-1}\end{align}" data-equation="eq:harmonic_mean">
<img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@2b632747053b9e357a4663369528fe62b29a6d55/lib/node_modules/@stdlib/stats/incr/hmean/docs/img/equation_harmonic_mean.svg" alt="Equation for the harmonic mean.">
<br>
</div>
<!-- </equation> -->
</section>
<!-- /.intro -->
<section class="usage">
## Usage
```javascript
var incrhmean = require( '@stdlib/stats/incr/hmean' );
```
#### incrhmean()
Returns an accumulator `function` which incrementally computes a [harmonic mean][harmonic-mean].
```javascript
var accumulator = incrhmean();
```
#### accumulator( \[x] )
If provided an input value `x`, the accumulator function returns an updated [harmonic mean][harmonic-mean]. If not provided an input value `x`, the accumulator function returns the current [harmonic mean][harmonic-mean].
```javascript
var accumulator = incrhmean();
var v = accumulator( 2.0 );
// returns 2.0
v = accumulator( 1.0 );
// returns ~1.33
v = accumulator( 3.0 );
// returns ~1.64
v = accumulator();
// returns ~1.64
```
</section>
<!-- /.usage -->
<section class="notes">
## Notes
- Input values are **not** type checked. If provided `NaN` or a value which, when used in computations, results in `NaN`, the accumulated value is `NaN` for **all** future invocations. If non-numeric inputs are possible, you are advised to type check and handle accordingly **before** passing the value to the accumulator function.
</section>
<!-- /.notes -->
<section class="examples">
## Examples
<!-- eslint no-undef: "error" -->
```javascript
var randu = require( '@stdlib/random/base/randu' );
var incrhmean = require( '@stdlib/stats/incr/hmean' );
var accumulator;
var v;
var i;
// Initialize an accumulator:
accumulator = incrhmean();
// For each simulated datum, update the harmonic mean...
for ( i = 0; i < 100; i++ ) {
v = randu() * 100.0;
accumulator( v );
}
console.log( accumulator() );
```
</section>
<!-- /.examples -->
<section class="links">
[harmonic-mean]: https://en.wikipedia.org/wiki/Harmonic_mean
</section>
<!-- /.links -->