Standard Deviation

Chi distribution standard deviation.

The standard deviation for a chi random variable is

sigma equals StartRoot k minus double-struck upper E left-bracket upper X right-bracket squared EndRoot

where k >= 0 is the degrees of freedom.

Usage

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

stdev( k )

Returns the standard deviation of a chi distribution with degrees of freedom k.

var v = stdev( 9.0 );
// returns ~0.697

v = stdev( 0.5 );
// returns ~0.521

If provided k < 0, the function returns NaN.

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

Examples

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

var k;
var v;
var i;

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