How to write the expression in matlab

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phoenix
phoenix 2018-6-28
评论： Star Strider 2018-6-28
How to write the expression : (2-s^500-3s^700)/(1-11s^400-20s^700)

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Star Strider
Star Strider 2018-6-28
First, add the required multiplicaiton operators, then:
s = tf('s');
H = (2-s^500-3*s^700)/(1-11*s^400-20*s^700)
H =
3 s^700 + s^500 - 2
-----------------------
20 s^700 + 11 s^400 - 1
Continuous-time transfer function.
This requires the Control System Toolbox, or a related Toolbox.
  2 个评论
phoenix
phoenix 2018-6-28
编辑：phoenix 2018-6-28
Thank you strider. What is the difference between the command s=tf('s') and s=tf('z')? Can the same thing be written as:(2-z^-500-3*z^-700)/(1-11*z^-400-20*z^-700)?
Star Strider
Star Strider 2018-6-28
The difference is that ideally you specify a sampling interval (or inter-sample interval) when you specify a discrete transfer function.
It otherwise works essentially the same:
z = tf('z');
H = (2-z^-500-3*z^-700)/(1-11*z^-400-20*z^-700)
H =
2 z^2300 - z^1800 - 3 z^1600
------------------------------
z^2300 - 11 z^1900 - 20 z^1600
Sample time: unspecified
Discrete-time transfer function.

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