function median( mu, beta ) {
	if (
		isnan( mu ) ||
		isnan( beta ) ||
		beta <= 0.0
	) {
		return NaN;
	}
	return mu - ( beta * LLN2 );
}
Returns the median for a Gumbel distribution with location `mu` and scale `beta`.

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

@example
var y = median( 0.0, 1.0 );
// returns ~0.367

@example
var y = median( 5.0, 2.0 );
// returns ~5.733

@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