How do you add a multiplication in the numerator of a transfer function.

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Sean Flanagan 2023-4-16

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评论： Paul 2023-4-18

The equation I need to represent as a transfer function is 5*e-ts/s+5. I coded as follows but my numerator returns as + 5 i need it to be * 5. Is there a way to achieve this?

clc
clear all
num=[exp(-1) 5];
den=[1 5];
g=tf(num,den)

g =

0.3679 s + 5

------------

s + 5

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回答（2 个）

Star Strider 2023-4-16

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编辑：Star Strider 2023-4-16

在 MATLAB Online 中打开

Perhaps this —

num=5*exp(-1);
den=[1 5];
g=tf(num,den)
g =
 
  1.839
  -----
  s + 5
 
Continuous-time transfer function.

The exponential function here is a constant. If you intend to introduce a delay, use InputDelay or one of the other options.

EDIT — (16 Apr 2023 at 10:44)

The transfer function would be —

num = 5;
den = [1 5];
g = tf(num, den, 'InputDelay',1)
g =
 
                5
  exp(-1*s) * -----
              s + 5
 
Continuous-time transfer function.

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Walter Roberson 2023-4-17

在 MATLAB Online 中打开

heaviside(1) is 1.

num = 5;
den = [1 5];
g = tf(num, den, 'InputDelay',1)
g =
 
                5
  exp(-1*s) * -----
              s + 5
 
Continuous-time transfer function.

Star Strider 2023-4-17

Of course, however it is a function of time, with the time argument not otherwise defined. This seems to be getting a bit less certain.

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Walter Roberson 2023-4-16

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s = tf('s');
g = 5 * exp(-t*s)/s + 5
Unrecognized function or variable 't'.

You cannot use an undefined or symbolic variable in a tf().

Are you sure that you want to add 5 to the delayed signal? Rather than using (s+5) as the denominator ?

https://www.mathworks.com/help/control/ug/time-delays-in-linear-systems.html

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Walter Roberson 2023-4-17

If you apply a unity step to s, the result would be the same as putting in the restriction that s >= 0

Paul 2023-4-18

What does "Tau is a unity step" mean? Tau is place holder for a number, isn't it?

How can a unity step be applied to s? s is the independent variable of the Laplace transform. In that same context, what does "restriction that s>=0" mean?

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