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

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@license Apache-2.0
Copyright (c) 2018 The Stdlib Authors.
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# incrmsum
> Compute a moving sum incrementally.
<section class="intro">
For a window of size `W`, the moving sum is defined as
<!-- <equation class="equation" label="eq:moving_sum" align="center" raw="s = \sum_{i=0}^{W-1} x_i" alt="Equation for the moving sum."> -->
<div class="equation" align="center" data-raw-text="s = \sum_{i=0}^{W-1} x_i" data-equation="eq:moving_sum">
<img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@49d8cabda84033d55d7b8069f19ee3dd8b8d1496/lib/node_modules/@stdlib/stats/incr/msum/docs/img/equation_moving_sum.svg" alt="Equation for the moving sum.">
<br>
</div>
<!-- </equation> -->
</section>
<!-- /.intro -->
<section class="usage">
## Usage
```javascript
var incrmsum = require( '@stdlib/stats/incr/msum' );
```
#### incrmsum( window )
Returns an accumulator `function` which incrementally computes a moving sum. The `window` parameter defines the number of values over which to compute the moving sum.
```javascript
var accumulator = incrmsum( 3 );
```
#### accumulator( \[x] )
If provided an input value `x`, the accumulator function returns an updated sum. If not provided an input value `x`, the accumulator function returns the current sum.
```javascript
var accumulator = incrmsum( 3 );
var sum = accumulator();
// returns null
// Fill the window...
sum = accumulator( 2.0 ); // [2.0]
// returns 2.0
sum = accumulator( 1.0 ); // [2.0, 1.0]
// returns 3.0
sum = accumulator( 3.0 ); // [2.0, 1.0, 3.0]
// returns 6.0
// Window begins sliding...
sum = accumulator( -7.0 ); // [1.0, 3.0, -7.0]
// returns -3.0
sum = accumulator( -5.0 ); // [3.0, -7.0, -5.0]
// returns -9.0
sum = accumulator();
// returns -9.0
```
</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 **at least** `W-1` 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.
- As `W` values are needed to fill the window buffer, the first `W-1` returned values are calculated from smaller sample sizes. Until the window is full, each returned value is calculated from all provided values.
</section>
<!-- /.notes -->
<section class="examples">
## Examples
<!-- eslint no-undef: "error" -->
```javascript
var randu = require( '@stdlib/random/base/randu' );
var incrmsum = require( '@stdlib/stats/incr/msum' );
var accumulator;
var v;
var i;
// Initialize an accumulator:
accumulator = incrmsum( 5 );
// For each simulated datum, update the moving sum...
for ( i = 0; i < 100; i++ ) {
v = randu() * 100.0;
accumulator( v );
}
console.log( accumulator() );
```
</section>
<!-- /.examples -->
<section class="links">
</section>
<!-- /.links -->