function median( mu, b ) {
	if (
		isnan( mu ) ||
		isnan( b ) ||
		b <= 0.0
	) {
		return NaN;
	}
	return mu;
}
Returns the median for a Laplace distribution with location `mu` and scale `b`.

@param {number} mu - location parameter
@param {PositiveNumber} b - scale parameter
@returns {number} median

@example
var y = median( 0.0, 1.0 );
// returns 0.0

@example
var y = median( 5.0, 2.0 );
// returns 5.0

@example
var y = median( NaN, 1.0 );
// returns NaN

@example
var y = median( 0.0, NaN );
// returns NaN

@example
var y = median( 0.0, 0.0 );
// returns NaN