Directional symmetry
Encyclopedia
Directional symmetry is roughly defined as "things going the same direction," and is to be distinguished from directional asymmetry, meaning "things going different directions."
The following formula
tests for directional symmetry:
If
is the actual signal and 
is the predicted one we have:
,
The following formula
Formula
In mathematics, a formula is an entity constructed using the symbols and formation rules of a given logical language....
tests for directional symmetry:
If
is the actual signal and is the predicted one we have:,