How to write the expression in matlab

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phoenix 2018-6-28

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https://ww2.mathworks.cn/matlabcentral/answers/407926-how-to-write-the-expression-in-matlab

评论： Star Strider 2018-6-28

采纳的回答： Star Strider

How to write the expression : (2-s^500-3s^700)/(1-11s^400-20s^700)

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Answer 1

Star Strider 2018-6-28

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https://ww2.mathworks.cn/matlabcentral/answers/407926-how-to-write-the-expression-in-matlab#answer_326711

在 MATLAB Online 中打开

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.

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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 2018-6-28

在 MATLAB Online 中打开

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.