where myDoubleArray contains 2.0, 4.0, 6.0, 8.0, 10.0, 12.0
then sigma is 14.0.
So I would conclude that the variance calculated by Commons Math is a sample variance not a population variance.

How would I calculate a sample variance using Commons Math?

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varp = (sum( x - M)^2) / n

where M = Mean of the x population