function mode( lambda ) {
	if ( isnan( lambda ) || lambda < 0.0 ) {
		return NaN;
	}
	return floor( lambda );
}
Returns the mode of a Poisson distribution.

@param {NonNegativeNumber} lambda - mean parameter
@returns {NonNegativeInteger} mode

@example
var v = mode( 9.0 );
// returns 9

@example
var v = mode( 1.0 );
// returns 1

@example
var v = mode( -0.2 );
// returns NaN

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