function rayleigh2( sigma ) {
		if (
			isnan( sigma ) ||
			sigma <= 0.0
		) {
			return NaN;
		}
		return rayleigh0( rand, sigma );
	}
Returns a pseudorandom number from a Rayleigh distribution with scale parameter `sigma`.

@private
@param {PositiveNumber} sigma - scale parameter
@returns {NonNegativeNumber} pseudorandom number

@example
var v = rayleigh2( 3.0 );
// returns <number>