Erf.scala

import scala.math

//Calculates the error function using Horner’s method.
class Erf {
  // constants
  val a1: Double =  0.254829592;
  val a2: Double = -0.284496736;
  val a3: Double =  1.421413741;
  val a4: Double = -1.453152027;
  val a5: Double =  1.061405429;
  val p: Double  =  0.3275911;

  def erf(x: Double): Double =  {
        // Save the sign of x
        val sign = if (x < 0) -1 else 1
        val absx =  math.abs(x)

        // A&S formula 7.1.26, rational approximation of error function
        val t = 1.0/(1.0 + p*absx);
        val y = 1.0 - (((((a5*t + a4)*t) + a3)*t + a2)*t + a1)*t*math.exp(-x*x);
        sign*y
    }
}

object Erf extends Erf
picomath

Scala
