Variance

Poisson distribution variance.

The variance for a Poisson random variable is

upper V a r left-parenthesis upper X right-parenthesis equals lamda

where λ is the mean parameter.

Usage

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

variance( lambda )

Returns the variance of a Poisson distribution with mean parameter lambda.

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

v = variance( 0.5 );
// returns 0.5

If provided lambda <= 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/poisson/variance' );

var lambda;
var v;
var i;

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