README.md (3503B)
1 <!-- 2 3 @license Apache-2.0 4 5 Copyright (c) 2018 The Stdlib Authors. 6 7 Licensed under the Apache License, Version 2.0 (the "License"); 8 you may not use this file except in compliance with the License. 9 You may obtain a copy of the License at 10 11 http://www.apache.org/licenses/LICENSE-2.0 12 13 Unless required by applicable law or agreed to in writing, software 14 distributed under the License is distributed on an "AS IS" BASIS, 15 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 16 See the License for the specific language governing permissions and 17 limitations under the License. 18 19 --> 20 21 # incrhmean 22 23 > Compute a [harmonic mean][harmonic-mean] incrementally. 24 25 <section class="intro"> 26 27 The [harmonic mean][harmonic-mean] of positive real numbers `x_0, x_1, ..., x_{n-1}` is defined as 28 29 <!-- <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."> --> 30 31 <div class="equation" align="center" data-raw-text="\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}" data-equation="eq:harmonic_mean"> 32 <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."> 33 <br> 34 </div> 35 36 <!-- </equation> --> 37 38 </section> 39 40 <!-- /.intro --> 41 42 <section class="usage"> 43 44 ## Usage 45 46 ```javascript 47 var incrhmean = require( '@stdlib/stats/incr/hmean' ); 48 ``` 49 50 #### incrhmean() 51 52 Returns an accumulator `function` which incrementally computes a [harmonic mean][harmonic-mean]. 53 54 ```javascript 55 var accumulator = incrhmean(); 56 ``` 57 58 #### accumulator( \[x] ) 59 60 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]. 61 62 ```javascript 63 var accumulator = incrhmean(); 64 65 var v = accumulator( 2.0 ); 66 // returns 2.0 67 68 v = accumulator( 1.0 ); 69 // returns ~1.33 70 71 v = accumulator( 3.0 ); 72 // returns ~1.64 73 74 v = accumulator(); 75 // returns ~1.64 76 ``` 77 78 </section> 79 80 <!-- /.usage --> 81 82 <section class="notes"> 83 84 ## Notes 85 86 - 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. 87 88 </section> 89 90 <!-- /.notes --> 91 92 <section class="examples"> 93 94 ## Examples 95 96 <!-- eslint no-undef: "error" --> 97 98 ```javascript 99 var randu = require( '@stdlib/random/base/randu' ); 100 var incrhmean = require( '@stdlib/stats/incr/hmean' ); 101 102 var accumulator; 103 var v; 104 var i; 105 106 // Initialize an accumulator: 107 accumulator = incrhmean(); 108 109 // For each simulated datum, update the harmonic mean... 110 for ( i = 0; i < 100; i++ ) { 111 v = randu() * 100.0; 112 accumulator( v ); 113 } 114 console.log( accumulator() ); 115 ``` 116 117 </section> 118 119 <!-- /.examples --> 120 121 <section class="links"> 122 123 [harmonic-mean]: https://en.wikipedia.org/wiki/Harmonic_mean 124 125 </section> 126 127 <!-- /.links -->