docs: public static final double correlation(double y1[],double y2[],int n) {
  
      int i;
      double av1 = 0.0, av2 = 0.0, y11 = 0.0, y22 = 0.0, y12 = 0.0, c;
      
      if (n <= 1) {
        return 1.0;
      }
      for (i = 0; i < n; i++) {
        av1 += y1[i];
        av2 += y2[i];
      }
      av1 /= (double) n;
      av2 /= (double) n;
      for (i = 0; i < n; i++) {
        y11 += (y1[i] - av1) * (y1[i] - av1);
        y22 += (y2[i] - av2) * (y2[i] - av2);
        y12 += (y1[i] - av1) * (y2[i] - av2);
      }
      if (y11 * y22 == 0.0) {
        c=1.0;
      } else {
        c = y12 / Math.sqrt(Math.abs(y11 * y22));
      }
      
      return c;
    }