Error in executing freqz command on LINUX server

I am trying to execute the command

[H,w] = freqz(b,a);

on the server machine of my university and it throws the following error: Bundle#165 start failed: libXcomposite.so.1: cannot open shared object file: No such file or directory.

I understand the error is due to the graphics. Could someone help me to solve this error? I do not need graphics, but just the FRF H and frequency vector w. I used the command matlab -nodisplay, but it doesn't help.

Answer 1

[David Goodmanson]

Hi Neuling,

If all else fails you could just write your own version. Something like

function [H w] = freqz1(b,a,n);
% parallels freqz for vectors of coefficients b,a, number of freqs n.
w = linspace(0,pi,n+1)';
w(end) = [];
Hn = zeros(n,1);
for k = 1:length(b)
    Hn = Hn + b(k)*exp(j*w*(1-k));
end
Hd = zeros(n,1);
for k = 1:length(a)
    Hd = Hd + a(k)*exp(j*w*(1-k));
end
H = Hn./Hd;
end

There are fancier ways, but the code just used a for loop.

As a test:

b = [1 2 3];
a = [3 4 5 6];
[H w] =    freqz(b,a);
[H1 w1] = freqz1(b,a,512);
max(abs(w-w1))           ans = 4.4409e-16
max(abs(H-H1))           ans = 2.7972e-15

[Neuling]

Thank you, it seems like that's the workaround