function erlang( rand, k, lambda ) {
	var prod;
	var i;
	prod = 1.0;
	for ( i = 0; i < k; i++ ) {
		prod *= rand();
	}
	return -(1.0/lambda) * ln( prod );
}
Returns a pseudorandom number drawn from an Erlang distribution.

@private
@param {PRNG} rand - PRNG for generating uniformly distributed numbers
@param {PositiveInteger} k - shape parameter
@param {PositiveNumber} lambda - rate parameter
@returns {number} pseudorandom number

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