Specifications

tf
16-220
• s = tf('s') to specify a TF model using a rational function in the Laplace
variable,
s.
•
z = tf('z',Ts) to specify a TF model with sample time Ts using a rational
function in the discrete-time variable,
z.
Once you specify either of these variables, you can specify TF models directly
as rational expressions in the variable
s or z by entering your transfer function
as a rational expression in either
s or z.
Conversion to Transfer Function
tfsys = tf(sys) converts an arbitrary SS or ZPK LTI model sys to transfer
function form. The output
tfsys (TF object) is the transfer function of sys.By
default,
tf uses zero tocompute thenumerators whenconvertingastate-space
model to transfer function form. Alternatively,
tfsys = tf(sys,'inv')
uses inversion formulas for state-space models to derive the numerators. This
algorithm is faster but less accurate for high-order models with low gain at
.
Examples Example 1
Create the two-output/one-input transfer function
with input
current and outputs torque and ang velocity.
To do this, type
num = {[1 1] ; 1}
den = {[1 2 2] ; [1 0]}
H = tf(num,den,'inputn','current',...
'outputn',{'torque' 'ang. velocity'},...
'variable','p')
s 0=
Hp
()
p 1+
p
2
2p 2++
-----------------------------
1
p
---
=