Hello, I'm having problems with the "freqs" or "freqz" function

I'm using a code that I found in MATLAB, to check if my code for another program is wrong. But this code that I found does not work either.

a = [1 0.4 1];
b = [0.2 0.3 1];
w = logspace(-1,1);
h = freqs(b,a,w);
mag = abs(h);
phase = angle(h);
phasedeg = phase*180/pi;
subplot(2,1,1)
loglog(w,mag)
grid on
xlabel('Frequency (rad/s)')
ylabel('Magnitude')
subplot(2,1,2)
semilogx(w,phasedeg)
grid on
xlabel('Frequency (rad/s)')
ylabel('Phase (degrees)')

This is the error I'm getting

Undefined function 'freqs' for input arguments of type 'double'.

Error in untitled4 (line 5)

h = freqs(b,a,w);

Do I need to activate the "freqs" function in MATLAB? I'm new to it, and don't have lots of experience generating code or using it. Thank you for any help.

Answer 1

[Walter Roberson]

You need to license and install the Signal Processing Toolbox.

If you purchased the MATLAB Student Suite then if I recall correctly that particular toolbox is included in the license; if you purchased MATLAB Student (not Suite) then it would not have been included by default.

[Javier Sanchez]

I activated the signal processing toolbox, but I still get the same error??

[Walter Roberson]

What shows up for you if you use the following commands?

ver('signal')

-----------------------------------------------------------------------------------------------------
MATLAB Version: 9.13.0.2182233 (R2022b) Update 4
MATLAB License Number: 0
Operating System: Linux 5.4.224-0504224-generic #202211101403 SMP Thu Nov 10 21:10:29 UTC 2022 x86_64
Java Version: Java 1.8.0_292-b10 with AdoptOpenJDK OpenJDK 64-Bit Server VM mixed mode
-----------------------------------------------------------------------------------------------------
Signal Processing Toolbox                             Version 9.1         (R2022b)

license('test', 'Signal_Toolbox')

ans = 1

Note: these exact names are important (though they are not case sensitive.) For example, testing 'signal' or 'signal_processing_toolbox' or 'signal toolbox' will fail.