Orientation conventions
There are two ways to represent a quadripole:
symmetrical convention: all the currents enter the quadripole. It is therefore seen as a reciever
from each side (see reference 9)
Asymmetrical convention: the quadripole is seen as a system with an ouput and an input. The current enters into the left input, and exits out of the right input. Therefore, the receiver convention is used on the left part, and the generator convention used on the right (see ref 6).
