function erfc2(y) {
    var xnum = P[1][8] * y;
    var xden = y;
    var i;

    for (i = 0; i < 7; i += 1) {
      xnum = (xnum + P[1][i]) * y;
      xden = (xden + Q[1][i]) * y;
    }

    var result = (xnum + P[1][7]) / (xden + Q[1][7]);
    var ysq = parseInt(y * 16) / 16;
    var del = (y - ysq) * (y + ysq);
    return Math.exp(-ysq * ysq) * Math.exp(-del) * result;
  }
Approximates the complement of the error function erfc() for
0.46875 <= x <= 4.0 using this function:
                      n
erfc(x) = e^(-x^2) * sum (p_j * x^j) / (q_j * x^j)
                     j=0