1 Introduction 7
A=
01
−6−7
,B=
0
1
,C=
γ
66
ρ
. (1.2)
According to theory of real number systems, clearly this system (1.2) is not
observable. But the determinant of observability matrix for RFS
det (C
T
,A
T
C
T
)
T
=
K
2
P
K
2
(T−T i)
T
2
i
T
3
is a nonzero member overF(z), and the system is observable overF(z), that
is, structurally observable. The points (such as
z=(2,1,3,1)) which make
this system unobservable overRform a set{z∈R
4
|det (C
T
,A
T
C
T
)
T
=0},
which is only a hypersurface in parameter spaceR
4
. BecauseK p,Ti,K,T
are physical parameters, it is impossible that their taken values are accurate enough to make det (C
T
,A
T
C
T
)
T
= 0. As for the real number system (1.2)
is unobservable, it can be understood that the man-made or mathematical constrainz=
z=(2,1,3,1) of the parameters makesT−T i=0,thatis,
det (C
T
,A
T
C
T
)
T
= 0. To a control system (physical system), if it is control-
lable and observable overF(z) (structural controllable and observable), then
it is always controllable and observable over the real field, or in the view of
robust, it is robust controllable and observable (it can be treated as a system
with certain structure and with uncertain parameters) for almost allz∈R
q
.
So researching and analyzing properties of systems and networks overF(z)
(structural properties) has more practicable meaning than that over the real
field.
Moreover, it is of theoretical value to research the structural properties
of systems overF(z). The real field is a subfield ofF(z); and SM, CSM,
one degree polynomial matrix and mixed matrix can be considered to be a
kind of matrices overF(z). So the criterions obtained overF(z)canbemore
generally used. For example, there is a conclusion overF(z) in [Lu, 2001]:
LetA=diag(A
1,...,Ak),B=(B
T
1
,...,B
T
k
)
T
,whereA iandB iaren i×ni
andn i×mmatrices overF(z) respectively,i=1,...,k, and det (λI−A i)and
det (λI−A
j) are relatively prime,iffi=j.Then(A,B) is controllable overF(z)
if and only if (A
i,Bi) is controllable overF(z). Corresponding conclusion over
the real field is contained in it. For example, letA=diag(λ
1,...,λn)and
B=(b
T
1
,...,b
T
n
)
T
are respectivelyn×nandn×mmatrices over the real
field (special RFM). If the eigenvalues ofAare different with each other,
that is,λ
iffi=λj,iffi=j,1ffii, jffin, it implies thatλ−λ iandλ−λ jare
relatively prime. By the above conclusion we have that (A, B) is controllable
if and only if (λ
i,bi) is controllable, that is,b iffi=0,i=1,...,n,whichisa
well-known criterion over the real field.
The properties overF(z) are only related to system structure, and the
systems with nonlinear elements maybe have the same or similar structure.