# incrrss
> Compute the [residual sum of squares][residual-sum-of-squares] (RSS) incrementally.
The [**residual sum of squares**][residual-sum-of-squares] (also referred to as the **sum of squared residuals** (SSR) and the **sum of squared errors** (SSE)) is defined as
## Usage
```javascript
var incrrss = require( '@stdlib/stats/incr/rss' );
```
#### incrrss()
Returns an accumulator `function` which incrementally computes the [residual sum of squares][residual-sum-of-squares].
```javascript
var accumulator = incrrss();
```
#### accumulator( \[x, y] )
If provided input values `x` and `y`, the accumulator function returns an updated [residual sum of squares][residual-sum-of-squares]. If not provided input values `x` and `y`, the accumulator function returns the current [residual sum of squares][residual-sum-of-squares].
```javascript
var accumulator = incrrss();
var r = accumulator( 2.0, 3.0 );
// returns 1.0
r = accumulator( -1.0, -4.0 );
// returns 10.0
r = accumulator( -3.0, 5.0 );
// returns 74.0
r = accumulator();
// returns 74.0
```
## 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 incrrss = require( '@stdlib/stats/incr/rss' );
var accumulator;
var v1;
var v2;
var i;
// Initialize an accumulator:
accumulator = incrrss();
// For each simulated datum, update the residual sum of squares...
for ( i = 0; i < 100; i++ ) {
v1 = ( randu()*100.0 ) - 50.0;
v2 = ( randu()*100.0 ) - 50.0;
accumulator( v1, v2 );
}
console.log( accumulator() );
```
[residual-sum-of-squares]: https://en.wikipedia.org/wiki/Residual_sum_of_squares
