# incrhmean
> Compute a [harmonic mean][harmonic-mean] incrementally.
The [harmonic mean][harmonic-mean] of positive real numbers `x_0, x_1, ..., x_{n-1}` is defined as
## Usage
```javascript
var incrhmean = require( '@stdlib/stats/incr/hmean' );
```
#### incrhmean()
Returns an accumulator `function` which incrementally computes a [harmonic mean][harmonic-mean].
```javascript
var accumulator = incrhmean();
```
#### accumulator( \[x] )
If provided an input value `x`, the accumulator function returns an updated [harmonic mean][harmonic-mean]. If not provided an input value `x`, the accumulator function returns the current [harmonic mean][harmonic-mean].
```javascript
var accumulator = incrhmean();
var v = accumulator( 2.0 );
// returns 2.0
v = accumulator( 1.0 );
// returns ~1.33
v = accumulator( 3.0 );
// returns ~1.64
v = accumulator();
// returns ~1.64
```
## 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 incrhmean = require( '@stdlib/stats/incr/hmean' );
var accumulator;
var v;
var i;
// Initialize an accumulator:
accumulator = incrhmean();
// For each simulated datum, update the harmonic mean...
for ( i = 0; i < 100; i++ ) {
v = randu() * 100.0;
accumulator( v );
}
console.log( accumulator() );
```
[harmonic-mean]: https://en.wikipedia.org/wiki/Harmonic_mean
