Covariance

aggregation-functions co-variance

syntax

• cov(a, b)
• cov(a, b, relation)

definition

• cov(a, b) results in a parameter with the co-variance of attributes a and b.
• cov(a, b, relation) results in an attribute with the co-variance of attributes a and b, grouped by relation. The domain-unit of the resulting attribute is the values-unit of the relation.

The value-type of the resulting data-item is float32 or float64.

applies to

• attribute a and b with Numeric value type
• relation with value type of the group CanBeDomainUnit

conditions

1. The value type of the arguments a and b must match.
2. The domain of arguments a, b and relation must match.

example

1. parameter<float32> covNrInhabitantsTemp                := 
   cov(float32(City/NrInhabitants), City/avgDailyTemperature); result = -156.25
2. attribute<float32> covNrInhabitantsTempRegion (Region) :=
   cov(
       float32(City/NrInhabitants)
     , City/avgDailyTemperature
     , City/RegionNr
  );

domain City, nr of rows = 7

domain Region, nr of rows = 5