Stream-based Linear Congruential Generator in Scala

LCG.scala

/** 
 * Linear Congruential Generator
 * 
 * This implementation allows you to grab an individual number by its index. It
 * also provides a stats object for displaying statistics about the lcg.
 * 
 * @see http://en.wikipedia.org/wiki/Linear_congruential_generator
 * @author Michael E. Cotterell <[email protected]>
 * @param a the multiplier
 * @param c the increment
 * @param m the modulus
 * @param seed start value
 */
case class LCG (a: Long, c: Long, m: Long, seed: Long) {

  import scala.language.postfixOps

  private val ref = this
  private val m_inverse = 1.0 / m.toDouble
  private var i: Int = 1
  private lazy val stream: Stream[Long] = 0L #:: seed #:: stream.zip(stream.tail).map({ case (e, last) => (a * last + c) % m })

  def gen: Double = stream({i += 1; i}).toDouble * m_inverse
  def get (idx: Int): Double = stream(idx + 2) * m_inverse
  def length: Int = i - 1

  object stats {

    lazy val samples: Array[Double] = stream.take(10000 + 2).drop(2).toArray.map( e => e * m_inverse )
    lazy val ms: Double = samples.map( e => e * e ).sum / samples.length
    lazy val mean: Double = samples.sum / samples.length
    lazy val variance: Double = ms - mean * mean

    override def toString: String = "%s.stats(samples = %5d, mean = %3.3f, variance = %3.3f)".format(ref, samples.length, mean, variance)

  } // test

} // LCG