Consider the following transfer matrix:
s = tf('s')
s =
s
Continuous-time transfer function.
G = [1/(s+2) 0; 0 1/((s+1)*(s+3))]
G =
From input 1 to output...
1
1: -----
s + 2
2: 0
From input 2 to output...
1: 0
1
2: -------------
s^2 + 4 s + 3
Continuous-time transfer function.
the calcultation of the normal rank of G is done by:
[z, nrank] = tzero(G)
z =
0x1 empty double column vector
and the result is
nrank = 1.
I was wondering, because in my understanding G will never lose rank for any 
and the normal rank should be equal to 2. So far, my observation is, that if the number of poles in the part transfer functions is equal, i.e.
G = [1/(s+2) 0; 0 1/(s+1)]
G =
From input 1 to output...
1
1: -----
s + 2
2: 0
From input 2 to output...
1: 0
1
2: -----
s + 1
Continuous-time transfer function.
[z, nrank] = tzero(G)
z =
0x1 empty double column vector
the result meets with my expectations (nrank = 2).
So my question is, am I missing something when using tzero or is there a general problem of understanding regarding the normal rank of a transfer matrix?
Many thanks in advance.
