how to convert a Laplace transform into a transfer function value
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>> A= tf([1 0],[1 1])
A =
s
-----
s + 1
Continuous-time transfer function.
>> p= feedback(A,1)
p =
s
-------
2 s + 1
Continuous-time transfer function.
>> laplace(t)
ans =
1/s^2
>> p= feedback(ans,1)
Error using feedback
Not enough input arguments.
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a = [2];
b = [1 0 0];
f= tf(a,b)
syms t;
d= laplace(2*t)
S= feedback(f,1)
D= feedback(d,1)
So, why the laplace tranform is not considered as a transfer function ???? If I have a time domain system, then how we can calculate the transfer function of that system.
回答（1 个）
The ‘d’ expression currently exists as a symbolic object. It needs to be transformed into a double value and then to a system object to work here —
a = [2];
b = [1 0 0];
f= tf(a,b)
syms t;
d= laplace(2*t) % Symbolic Object
[dn,dd] = numden(d) % Get Numerator & Denominator
dnp = double(sym2poly(dn)) % Convert To Polynomial Vectors & 'double' Values (From Symbolic Variables)
ddp = double(sym2poly(dd)) % Convert To Polynomial Vectors & 'double' Values (From Symbolic Variables)
dtf = tf(dnp, ddp) % Create AS Control System Toolbos 'system' Object
S= feedback(f,1)
D= feedback(dtf,1)
.
See the documentation on the relevant Symbolic Toolbox functions numden, sym2poly, and double for details.
.
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2023-1-5
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