function gumbel2( mu, beta ) {
		if (
			isnan( mu ) ||
			isnan( beta ) ||
			beta <= 0.0
		) {
			return NaN;
		}
		return gumbel0( rand, mu, beta );
	}
Returns pseudorandom number drawn from a Gumbel distribution.

@private
@param {number} mu - mean
@param {PositiveNumber} beta - scale parameter
@returns {number} pseudorandom number

@example
var v = gumbel2( 0.0, 2.0 );
// returns <number>

@example
var v = gumbel2( 0.0, -1.0 );
// returns NaN