function erlang2( k, lambda ) {
		if (
			isnan( k ) ||
			isnan( lambda ) ||
			!isPositiveInteger( k ) ||
			lambda <= 0.0
		) {
			return NaN;
		}
		return erlang0( rand, k, lambda );
	}
Returns a pseudorandom number drawn from an Erlang distribution.

@private
@param {PositiveInteger} k - shape parameter
@param {PositiveNumber} lambda - rate parameter
@returns {number} pseudorandom number

@example
var v = erlang2( 2, 1.0 );
// returns <number>

@example
var v = erlang2( NaN, 1.0 );
// returns NaN

v = erlang2( 2, NaN );
// returns NaN

v = erlang2( 3.14, 1.0 );
// returns NaN

v = erlang2( 2, 0.0 );
// returns NaN