Harmonic Mean

In mathematics, the harmonic mean is a kind of average, one of the Pythagorean means, normally used only for positive arguments and applied especially to ratios and rates such as speeds. It is defined as the reciprocal of the arithmetic mean of the reciprocals of the numbers, so the harmonic mean of 1, 4, and 4 is 2, found by averaging the reciprocals 1/1, 1/4, and 1/4 and taking the reciprocal of that average. Because the harmonic mean of a list of numbers tends strongly toward the least elements of the list, it mitigates the impact of large outliers while aggravating the impact of small ones, which makes it useful in situations where extreme values should not dominate the result.