Variance

Chi distribution variance.

The variance for a chi random variable is

upper V a r left-parenthesis upper X right-parenthesis equals k minus double-struck upper E left-bracket upper X right-bracket squared

where k >= 0 is the degrees of freedom.

Usage

var variance = require( '@stdlib/math/base/dists/chi/variance' );

variance( k )

Returns the variance of a chi distribution with degrees of freedom k.

var v = variance( 9.0 );
// returns ~0.485

v = variance( 0.5 );
// returns ~0.272

If provided k < 0, the function returns NaN.

var v = variance( -1.0 );
// returns NaN

Examples

var randu = require( '@stdlib/random/base/randu' );
var round = require( '@stdlib/math/base/special/round' );
var variance = require( '@stdlib/math/base/dists/chi/variance' );

var k;
var v;
var i;

for ( i = 0; i < 10; i++ ) {
    k = randu() * 20.0;
    v = variance( k );
    console.log( 'k: %d, Var(X,k): %d', k.toFixed( 4 ), v.toFixed( 4 ) );
}