Find poles and zeros of transfer function

A = [-3 5 -7 0; 0.5 -1.5 0.5 -7.5;-5 0 -3 0; -0.5 -5 0 .7];
B = [1 0 0; 0 -1 0; -2 0 0; 0 1 2];
C = [1 0 0 0; 0 -1 0 0];
D = [-1 0 0; 2 0 0];

S = ss(A, B, C, D)
G = tf(SS)

% Compute Poles
poles = eig(A)

%Compute Zeros
zeros = tzero(A,B,C,D)

Gss = minreal( ss( S ) )

When I run this code i get the following error:

Error using ss (line 278)

The "D" matrix must be a numeric array with no Inf's or NaN's.

Error in Q5 (line 23)

Gss = minreal( ss( S ) );

[Paul]

Why did you delete the code from your question?

And why did you change the question itself? It used to be Find poles and zeros of a transfer function

[Paul]

I don't think this was the original code for this question ....

Answer 1

[Paul]

That error shows up because minreal() and ss(), etc. are functions in the Control System Toolbox. Those functions cannot accept sym objects like Gsys.

Even if you just use Control System Toolbox functions, you're going to have troubles because the elements of Gsys are improper (degree of numerator > degree of denominator).

Also, I thought the Smith form only applies to the "numerator" of the transfer function matrix, not the entire tranfser function matrix.

Also, doesn't that call to smithForm throw an error because Gsys isn't square?

What exactly are you you trying to do? Find the Smith-McMillan form of Gsys?

[Siddhanth Sunil Shah]

Sorry that I was not clear. Yes the MATLAB throws an error since Gsys is not square and a 2x3 sym.

And I am trying to figure out a way to find the Smith-McMillan form of Gsys and also a method to derive the Smith Form for non-square matrix but unable to succeed.

After finding the Smith-McMillan form of Gsys, I want to compute the poles and zeros of that form

Best Regards,

Siddhanth

[Paul]

If Gsys were square, then it seems like it should be doable. Here's a simple example.

Define a simple transfer function matrix

syms s
Gsys(s) = [s/((s + 1)^2*(s + 2)^2),  s/(s + 2)^2; -s/(s + 2)^2, -s/(s + 2)^2];

Get the least common denominator of all the terms

[num,den] = numden(Gsys);
d(s) = lcm(den)

d(s) = 

Compute N(s) from d(s) and Gsys(s)

N(s) = simplify(d(s)*Gsys(s))

N(s) = 

Get the Smith form of N(s)

[U1,U2,L] = smithForm(N(s));

The Smith-McMillan form of Gsys is then

M(s) = simplify(L/d(s))

M(s) = 

Get the zeros and the poles

[num,den] = numden(M(s));
for ii = 1:2
smzeros{ii} = solve(num(ii,ii),s).';
smpoles{ii} = solve(den(ii,ii),s).';
end

smzeros = [smzeros{:}]

smzeros = 

smpoles = [smpoles{:}]

smpoles = 

But your Gsys isn't square. Don't know why smithForm does not handle non square, polynomial matrices.

Answer 2

[Emiliano martin]

clear all 
close all 
clc

s=tf('s');

TF_Sys=8/s(2*s+1)*(.05*s+1); 

figure (1)
pzmap(TF_Sys)


is giving me an arror, please help!!