SigmaXY Command

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SigmaXY( <List of Points> )
Calculates the sum of the products of the x- and y-coordinates.
Example: You can work out the covariance of a list of points using SigmaXY(list)/Length(list) - MeanX(list) * MeanY(list).


SigmaXY( <List of x-coordinates>, <List of y-coordinates> )
Calculates the sum of the products of the x- and y-coordinates.
Example: Let A = (-3, 4), B = (-1, 4), C = (-2, 3) and D = (1, 3) be points. {x(A), x(B), x(C), x(D)} yields the x-coordinates of the points in a list list1 = {-3, -1, -2, 1} and {y(A), y(B), y(C), y(D)} yields the y-coordinates of the points in a list list2 = {4, 4, 3, 3}. Command SigmaXY(list1, list2) yields a = -19.
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