tt_GEOMEAN function

Implementation

dynamic tt_GEOMEAN(List<dynamic> values) {
  final n = values.length;
  if (n == 0) return 0.0;
  double logSum = 0;
  for (final v in values) {
    final x = varToDouble(v);
    if (x <= 0) return 0.0;
    logSum += log(x);
  }
  final r = exp(logSum / n);
  // @@@ a log/exp round trip produces tiny floating-point noise (e.g.
  //     (1*3*9)^(1/3) is theoretically exactly 3, but actually computes
  //     to 3.0000000000000004) -- rounded to 12 decimal places to clear
  //     the noise. The log/exp algorithm itself is kept (rather than
  //     switching to direct multiply-then-root) because with many input
  //     values at large magnitudes, direct multiplication can overflow;
  //     log/exp is more numerically robust.
  return double.parse(r.toStringAsFixed(12));
}