@stdlib/stats-incr-ewvariance
v0.2.2
Published
Compute an exponentially weighted variance incrementally.
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increwvariance
Compute an exponentially weighted variance incrementally.
An exponentially weighted variance can be defined recursively as
where μ
is the exponentially weighted mean.
Installation
npm install @stdlib/stats-incr-ewvariance
Usage
var increwvariance = require( '@stdlib/stats-incr-ewvariance' );
increwvariance( alpha )
Returns an accumulator function
which incrementally computes an exponentially weighted variance, where alpha
is a smoothing factor between 0
and 1
.
var accumulator = increwvariance( 0.5 );
accumulator( [x] )
If provided an input value x
, the accumulator function returns an updated variance. If not provided an input value x
, the accumulator function returns the current variance.
var accumulator = increwvariance( 0.5 );
var v = accumulator();
// returns null
v = accumulator( 2.0 );
// returns 0.0
v = accumulator( 1.0 );
// returns 0.25
v = accumulator( 3.0 );
// returns 0.6875
v = accumulator();
// returns 0.6875
Notes
- Input values are not type checked. If provided
NaN
or a value which, when used in computations, results inNaN
, the accumulated value isNaN
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
var randu = require( '@stdlib/random-base-randu' );
var increwvariance = require( '@stdlib/stats-incr-ewvariance' );
var accumulator;
var v;
var i;
// Initialize an accumulator:
accumulator = increwvariance( 0.5 );
// For each simulated datum, update the exponentially weighted variance...
for ( i = 0; i < 100; i++ ) {
v = randu() * 100.0;
accumulator( v );
}
console.log( accumulator() );
See Also
@stdlib/stats-incr/ewmean
: compute an exponentially weighted mean incrementally.@stdlib/stats-incr/ewstdev
: compute an exponentially weighted standard deviation incrementally.@stdlib/stats-incr/variance
: compute an unbiased sample variance incrementally.@stdlib/stats-incr/mvariance
: compute a moving unbiased sample variance incrementally.
Notice
This package is part of stdlib, a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.
For more information on the project, filing bug reports and feature requests, and guidance on how to develop stdlib, see the main project repository.
Community
License
See LICENSE.
Copyright
Copyright © 2016-2024. The Stdlib Authors.