# incrsum
> Compute a sum incrementally.
## Usage
```javascript
var incrsum = require( '@stdlib/stats/incr/sum' );
```
#### incrsum()
Returns an accumulator `function` which incrementally computes a sum.
```javascript
var accumulator = incrsum();
```
#### 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 = incrsum();
var sum = accumulator( 2.0 );
// returns 2.0
sum = accumulator( 1.0 );
// returns 3.0
sum = accumulator( 3.0 );
// returns 6.0
sum = accumulator();
// returns 6.0
```
## 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.
- For long running accumulations or accumulations of large numbers, care should be taken to prevent overflow.
## Examples
```javascript
var randu = require( '@stdlib/random/base/randu' );
var incrsum = require( '@stdlib/stats/incr/sum' );
var accumulator;
var v;
var i;
// Initialize an accumulator:
accumulator = incrsum();
// For each simulated datum, update the sum...
for ( i = 0; i < 100; i++ ) {
v = randu() * 100.0;
accumulator( v );
}
console.log( accumulator() );
```
* * *
## References
- Klein, Andreas. 2005. "A Generalized Kahan-Babuška-Summation-Algorithm." _Computing_ 76 (3): 279–93. doi:[10.1007/s00607-005-0139-x][@klein:2005a].
[@klein:2005a]: https://doi.org/10.1007/s00607-005-0139-x
