Specifications

nyquist
16-157
[re,im,w] = nyquist(sys)
[re,im] = nyquist(sys,w)
return the real and imaginary parts of the frequency response at the
frequencies
w (in rad/sec). re and im are 3-D arrays with the frequency as last
dimension (see “Arguments” below for details).
Arguments The output arguments re and im are 3-D arrays with dimensions
For SISO systems, the scalars
re(1,1,k) and im(1,1,k) are the real and
imaginary parts of the response at the frequency .
For MIMO systems with transfer function ,
re(:,:,k) and im(:,:,k)
give the real and imaginary parts of (both arrays with as many rows
as outputs and as many columns as inputs). Thus,
where is the transfer function from input to output .
Example Plot the Nyquist response of the system
H = tf([2 5 1],[1 2 3])
number of outputs
()
number of inputs
()×
length of w()×
ω
k
w(k)=
re(1,1,k) Re hj
ω
k
()()
=
im(1,1,k) Im hj
ω
k
()()
=
Hs
()
Hj
ω
k
()
re(i,j,k) Re h
ij
j
ω
k
()()
=
im(i,j,k) Im h
ij
j
ω
k
()()
=
h
ij
j
i
Hs
()
2s
2
5s 1++
s
2
2s 3++
-------------------------------
=