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# incrmsumabs

> Compute a moving sum of absolute values incrementally.

<section class="intro">

For a window of size `W`, the moving sum of absolute values is defined as

<!-- <equation class="equation" label="eq:moving_sum_absolute_values" align="center" raw="s = \sum_{i=0}^{W-1} |x_i|" alt="Equation for the moving sum of absolute values."> -->

<div class="equation" align="center" data-raw-text="s = \sum_{i=0}^{W-1} |x_i|" data-equation="eq:moving_sum_absolute_values">
    <img src="https://cdn.rawgit.com/stdlib-js/stdlib/27e2a43c70db648bb5bbc3fd0cdee050c25adc0b/lib/node_modules/@stdlib/stats/incr/msumabs/docs/img/equation_moving_sum_absolute_values.svg" alt="Equation for the moving sum of absolute values.">
    <br>
</div>

<!-- </equation> -->

</section>

<!-- /.intro -->

<section class="usage">

## Usage

```javascript
var incrmsumabs = require( '@stdlib/stats/incr/msumabs' );
```

#### incrmsumabs( window )

Returns an accumulator `function` which incrementally computes a moving sum of absolute values. The `window` parameter defines the number of values over which to compute the moving sum.

```javascript
var accumulator = incrmsumabs( 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 = incrmsumabs( 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 11.0

sum = accumulator( -5.0 ); // [3.0, -7.0, -5.0]
// returns 15.0

sum = accumulator();
// returns 15.0
```

</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 incrmsumabs = require( '@stdlib/stats/incr/msumabs' );

var accumulator;
var v;
var i;

// Initialize an accumulator:
accumulator = incrmsumabs( 5 );

// For each simulated datum, update the moving sum...
for ( i = 0; i < 100; i++ ) {
    v = ( randu()*100.0 ) - 50.0;
    accumulator( v );
}
console.log( accumulator() );
```

</section>

<!-- /.examples -->

<section class="links">

</section>

<!-- /.links -->
