Receiving error "Unrecognized function or variable 'tf'" even though I have the Signal Processing Toolbox installed.

I am trying to produce a bode plot using the tf function. My code is as follows:

num = [10000000000000000000000000000 7000000000000000000000000000000];

den = [1 7540690 21324854073600 26807731666619904000 12647107451415440994336768 10730685839764156310146252800];

G = tf(num, den)

bode(G),grid;

The error is in line 4. I am receiving the error message despite having the Signal Processing Toolbox installed. When I type "ver" into the command window I get this:

MATLAB Version: 9.10.0.1669831 (R2021a) Update 2

Operating System: Microsoft Windows 10 Home Version 10.0 (Build 19042)

Java Version: Java 1.8.0_202-b08 with Oracle Corporation Java HotSpot(TM) 64-Bit Server VM mixed mode

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MATLAB Version 9.10 (R2021a)

Signal Processing Toolbox Version 8.6 (R2021a)

I am new to MATLAB so I would appreciate any pointers. Thank you.

[Matthew Crain]

Nevermind! I found that I needed the Control Systems Toolbox add-on. Apparently the tf function is not a part of the Signals Processing Toolbox. The more you know!

[Brian Mcnulty]

the 'tf' command is not recognized and the command window provides a reccomendation instead.

I have all the correct toolboxes installed, however, the error persists.

What can I do to alleviate this issue. Any suggestions would be greatly appreciated. Thank you in advance.

Answer 1

[Steven Lord]

which -all tf

/MATLAB/toolbox/control/ctrlmodels/@tf/tf.m                 % tf constructor
/MATLAB/toolbox/mpc/mpc/@mpc/tf.m                           % Shadowed mpc method
/MATLAB/toolbox/control/ctrlmodels/@DynamicSystem/tf.m      % Shadowed DynamicSystem method
/MATLAB/toolbox/ident/ident/@idParametric/tf.m              % Shadowed idParametric method
/MATLAB/toolbox/shared/controllib/engine/@StaticModel/tf.m  % Shadowed StaticModel method

There are several functions named tf in various MathWorks products, but most of them are intended for use in converting some sort of other object into a tf object. As you have learned the tf function in Control System Toolbox (the first on that list) is what you should use for creating a tf object from raw numeric data.