# SigmaXY Command

From GeoGebra Manual

Revision as of 12:32, 16 July 2013 by MagdalenaSophieF (talk | contribs)

- 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*.