SigmaXX Command

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SigmaXX( <List of Points> )
Calculates the sum of squares of the x-coordinates of the given points.
Example: Let list1 = { (-3, 4), (-1, 4), (-2, 3), (1, 3), (2, 2), (1, 5) } be a list of points. SigmaXX[ list1 ] yields the value 20.


SigmaXX( <List of Raw Data> )
Calculates the sum of squares of the given numbers.
Example: In order to work out the variance of a list you may use SigmaXX[list] / Length[list] - Mean[list]^2.


SigmaXX( <List of Numbers>, <List of Frequencies> )
Calculates the weighted sum of squares of the given numbers.
Example: Let list1 = {3, 2, 4, 3, 3, 2, 1, 1, 2, 3, 3, 4, 5, 3, 2, 1, 1, 2, 3} be a list of numbers. Unique[ list1 ] yields list2 = {1, 2, 3, 4, 5} and Frequency[ list1 ] yields list3 = {4, 5, 7, 2, 1}. Command SigmaXX[ list2, list3 ] yields the value 144.
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