function mode( lambda ) {
	if ( isnan( lambda ) || lambda <= 0.0 ) {
		return NaN;
	}
	return 0;
}
Returns the mode of a Planck distribution.

@param {PositiveNumber} lambda - shape parameter
@returns {NonNegativeInteger} mode

@example
var v = mode( 0.1 );
// returns 0

@example
var v = mode( 1.5 );
// returns 0

@example
var v = mode( -1.1 );
// returns NaN

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