# Difference between revisions of "SigmaXY Command"

From GeoGebra Manual

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− | ; SigmaXY[List of Points]: Calculates the sum of the products of the ''x''- and ''y''-coordinates. | + | ; SigmaXY[ <List of Points> ] |

+ | :Calculates the sum of the products of the ''x''- and ''y''-coordinates. | ||

:{{Example|1=You can work out the covariance of a list of points using <code>SigmaXY[list]/Length[list] - MeanX[list] * MeanY[list]</code>.}} | :{{Example|1=You can work out the covariance of a list of points using <code>SigmaXY[list]/Length[list] - MeanX[list] * MeanY[list]</code>.}} | ||

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+ | ;SigmaXY[ <List of x-coordinates>, <List of y-coordinates> ] | ||

+ | :Calculates the sum of the products of the ''x''- and ''y''-coordinates. | ||

+ | :{{Example|1=Let <code><nowiki>A = (-3, 4)</nowiki></code>, <code><nowiki>B = (-1, 4)</nowiki></code>, <code><nowiki>C = (-2, 3)</nowiki></code> and <code><nowiki>D = (1, 3)</nowiki></code> be points. <code><nowiki>{x(A), x(B), x(C), x(D)}</nowiki></code> yields the x-coordinates of the points in a list ''list1 = {-3, -1, -2, 1}'' and <code><nowiki>{y(A), y(B), y(C), y(D)}</nowiki></code> yields the y-coordinates of the points in a list ''list2 = {4, 4, 3, 3}''. Command <code><nowiki>SigmaXY[ list1, list2 ]</nowiki></code> yields ''a = -19''.}} |

## Revision as of 12:32, 16 July 2013

- 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*.