Specifications

2 LTI Models
2-34
Sampling time: unspecified
The same result is obtained by using the Variable property.
h = tf(1,[1 –1],'var','z')
In operations that combine several discrete-time models, all specified sample
times must be identical, and the resulting discrete-time model inherits this
common sample time. The sample time of the resultant model is unspecified if
all operands have unspecified sample times. With this inheritance rule for
Ts,
the following two models are equivalent.
tf(0.1,[1 –1],0.1) + tf(1,[1 0.5],–1)
and
tf(0.1,[1 –1],0.1) + tf(1,[1 0.5],0.1)
Note that
tf(0.1,[1 –1],0.1) + tf(1,[1 0.5],0.5)
returns an error message.
??? Error using ==> lti/plus
In SYS1+SYS2, both models must have the same sample time.
Caution: Resettingthesampletimeofacontinuous-timeLTImodelsys from
zero to a nonzero value does not discretize the original model
sys.The
command
set(sys,'Ts',0.1)
only affects the Ts property and does not alter the remaining model data. Use
c2d and d2c to perform continuous-to-discrete and discrete-to-continuous
conversions. For example, use
sysd = c2d(sys,0.1)
to discretize a continuous system sys at a 10Hz sampling rate.
Use
d2d to change the sample time of a discrete-time system and resample it.