•** ****transpose or dual system
**

or equivalently

• **conjugate system
**

or
equivalently

In particular, we
have *G*(j**w**):=*[*G(j**w**)*]**=G**˜(**j**w**).*

•** inverse system:**

Let *D**+* denote a right (left) inverse of *D* if *D* has full row

(column) rank.
Then

is a right (left)
inverse of *G*, I.e, *GG**+**=I* (*G**+**G=I)*.