function laplace2( mu, b ) {
		if (
			isnan( mu ) ||
			isnan( b ) ||
			b <= 0.0
		) {
			return NaN;
		}
		return laplace0( rand, mu, b );
	}
Returns a pseudorandom number drawn from a Laplace (double exponential) distribution.

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

@example
var v = laplace2( 0.0, 2.0 );
// returns <number>

@example
var v = laplace2( 0.0, -1.0 );
// returns NaN