Complex transfer function, 's' to 'jw' conversion

Hi,

I have a big size transfer function in S-domain and I need to replace the 's' with 'jw' in that function (conver s to complex mode). Can anyone help me?

[Azzi Abdelmalek]

Give a short example, and tell what should be the result?

[lounis chehrit]

what about a signal which is for example:

Real(X(s))=34cos(2*pi*s/20) + 2cos(4*pi*s)

Imag(X(s))=21 sin(2*pi*s/3) + 20 sin(15*pi*s/12)

how can i find the transfer function? without the complex J.

And how can i compute the laplace inv without errors please ?

Answer 1

[Azzi Abdelmalek]

If you have the transfer function G, you can get the numerator and denominator by using getdata function, then use this code

w=-10:0.1:10  % Frequency vector
N=[1 2] % Transfer function numerator
D=[1 3 2] % Transfer function Denominator
syms w
g=poly2sym(N,i*w)/poly2sym(D,i*w)
w=-10:0.1:10
h=double(subs(g))
plot(abs(h))

[Mehdi Ghasem Moghadam]

Hi I think something is wrong. It does not work.

[Victor Manuel Chan Ortiz]

You can do:

g=poly2sym(N,s)/poly2sym(D,s);

g=subs(g,s,w*1i)

And replace w with the value that you need

[lounis chehrit]

what about a signal which is for example:

Real(X(s))=34cos(2*pi*s/20) + 2cos(4*pi*s)

Imag(X(s))=21 sin(2*pi*s/3) + 20 sin(15*pi*s/12)

how can i find the transfer function? without the complex J.

And how can i compute the laplace inv without errors please ?