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# incrmeanabs2

> Compute an [arithmetic mean][arithmetic-mean] of squared absolute values incrementally.

<section class="intro">

The [arithmetic mean][arithmetic-mean] of squared absolute values is defined as

<!-- <equation class="equation" label="eq:arithmetic_mean_squared_absolute_values" align="center" raw="m = \frac{1}{n} \sum_{i=0}^{n-1} x_i^2" alt="Equation for the arithmetic mean of squared absolute values."> -->

<div class="equation" align="center" data-raw-text="m = \frac{1}{n} \sum_{i=0}^{n-1} x_i^2" data-equation="eq:arithmetic_mean_squared_absolute_values">
    <img src="https://cdn.rawgit.com/stdlib-js/stdlib/d08c5f0a491ba12729c84e40455fb75cf8666874/lib/node_modules/@stdlib/stats/incr/meanabs2/docs/img/equation_arithmetic_mean_squared_absolute_values.svg" alt="Equation for the arithmetic mean of squared absolute values.">
    <br>
</div>

<!-- </equation> -->

</section>

<!-- /.intro -->

<section class="usage">

## Usage

```javascript
var incrmeanabs2 = require( '@stdlib/stats/incr/meanabs2' );
```

#### incrmeanabs2()

Returns an accumulator `function` which incrementally computes an [arithmetic mean][arithmetic-mean] of squared absolute values.

```javascript
var accumulator = incrmeanabs2();
```

#### accumulator( \[x] )

If provided an input value `x`, the accumulator function returns an updated mean. If not provided an input value `x`, the accumulator function returns the current mean.

```javascript
var accumulator = incrmeanabs2();

var m = accumulator( 2.0 );
// returns 4.0

m = accumulator( -1.0 );
// returns 2.5

m = accumulator( -3.0 );
// returns ~4.67

m = accumulator();
// returns ~4.67
```

</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 incrmeanabs2 = require( '@stdlib/stats/incr/meanabs2' );

var accumulator;
var v;
var i;

// Initialize an accumulator:
accumulator = incrmeanabs2();

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

</section>

<!-- /.examples -->

<section class="links">

[arithmetic-mean]: https://en.wikipedia.org/wiki/Arithmetic_mean

</section>

<!-- /.links -->
