public static double incompleteGammaComplement()

in samoa-api/src/main/java/org/apache/samoa/moa/core/Statistics.java [628:682]

• 45 lines of code
• 9 McCabe index (conditional complexity)

  public static double incompleteGammaComplement(double a, double x) {

    double ans, ax, c, yc, r, t, y, z;
    double pk, pkm1, pkm2, qk, qkm1, qkm2;

    if (x <= 0 || a <= 0)
      return 1.0;

    if (x < 1.0 || x < a)
      return 1.0 - incompleteGamma(a, x);

    ax = a * Math.log(x) - x - lnGamma(a);
    if (ax < -MAXLOG)
      return 0.0;

    ax = Math.exp(ax);

    /* continued fraction */
    y = 1.0 - a;
    z = x + y + 1.0;
    c = 0.0;
    pkm2 = 1.0;
    qkm2 = x;
    pkm1 = x + 1.0;
    qkm1 = z * x;
    ans = pkm1 / qkm1;

    do {
      c += 1.0;
      y += 1.0;
      z += 2.0;
      yc = y * c;
      pk = pkm1 * z - pkm2 * yc;
      qk = qkm1 * z - qkm2 * yc;
      if (qk != 0) {
        r = pk / qk;
        t = Math.abs((ans - r) / r);
        ans = r;
      } else
        t = 1.0;

      pkm2 = pkm1;
      pkm1 = pk;
      qkm2 = qkm1;
      qkm1 = qk;
      if (Math.abs(pk) > big) {
        pkm2 *= biginv;
        pkm1 *= biginv;
        qkm2 *= biginv;
        qkm1 *= biginv;
      }
    } while (t > MACHEP);

    return ans * ax;
  }