Time complexity of Math.Sqrt()?

问题:

How can I find the complexity of this function?

private double EuclideanDistance(MFCC.MFCCFrame vec1, MFCC.MFCCFrame vec2)
{
  double Distance = 0.0;
  for (int K = 0; K < 13; K++)
     Distance += (vec1.Features[K] - vec2.Features[K]) * (vec1.Features[K] - vec2.Features[K]);
  return Math.Sqrt(Distance);
}

I know that the below section is O(1):

double Distance = 0.0;
for (int K = 0; K < 13; K++)
   Distance += (vec1.Features[K]-vec2.Features[K])*(vec1.Features[K]-vec2.Features[K]);

But I can't figure out what the complexity of Math.Sqrt() is.

回答1:

You can consider it O(1):

In other words, Math.Sqrt() translates to a single floating point machine code instruction

source: c# Math.Sqrt Implementation