function variance( mu ) {
	if ( isnan( mu ) ) {
		return NaN;
	}
	return 0.0;
}
Returns the variance of a degenerate distribution.

@param {number} mu - constant value of distribution
@returns {NonNegativeNumber} variance

@example
var v = variance( 0.1 );
// returns 0.0

@example
var v = variance( 0.5 );
// returns 0.0

@example
var v = variance( 10.0 );
// returns 0.0

@example
var v = variance( NaN );
// returns NaN