Variance
The variance for a Poisson random variable is
where λ is the mean parameter.
Usage
var variance = require( '@stdlib/stats/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/stats/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 ) );
}