# incrrmse
> Compute the [root mean squared error][root-mean-squared-error] (RMSE) incrementally.
The [**root mean squared error**][root-mean-squared-error] (also known as the **root mean square error** (RMSE) and **root mean square deviation** (RMSD)) is defined as
## Usage
```javascript
var incrrmse = require( '@stdlib/stats/incr/rmse' );
```
#### incrrmse()
Returns an accumulator `function` which incrementally computes the [root mean squared error][root-mean-squared-error].
```javascript
var accumulator = incrrmse();
```
#### accumulator( \[x, y] )
If provided input values `x` and `y`, the accumulator function returns an updated [root mean squared error][root-mean-squared-error]. If not provided input values `x` and `y`, the accumulator function returns the current [root mean squared error][root-mean-squared-error].
```javascript
var accumulator = incrrmse();
var r = accumulator( 2.0, 3.0 );
// returns 1.0
r = accumulator( -1.0, -4.0 );
// returns ~2.24
r = accumulator( -3.0, 5.0 );
// returns ~4.97
r = accumulator();
// returns ~4.97
```
## 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.
## Examples
```javascript
var randu = require( '@stdlib/random/base/randu' );
var incrrmse = require( '@stdlib/stats/incr/rmse' );
var accumulator;
var v1;
var v2;
var i;
// Initialize an accumulator:
accumulator = incrrmse();
// For each simulated datum, update the root mean squared error...
for ( i = 0; i < 100; i++ ) {
v1 = ( randu()*100.0 ) - 50.0;
v2 = ( randu()*100.0 ) - 50.0;
accumulator( v1, v2 );
}
console.log( accumulator() );
```
[root-mean-squared-error]: https://en.wikipedia.org/wiki/Root-mean-square_deviation
