Unrecognized function from Robust Control Toolbox

Hello,

I am facing the problem of not being able to use functions from the Robust Control Toolbox (I am using Ubuntu 18.04), e.g.,

>> mixsyn
Unrecognized function or variable 'mixsyn'.

Both the help mixsyn and which mixsyn commands work and give the correct information/path, e.g.,

>> help mixsyn
--- help for DynamicSystem/mixsyn ---

 mixsyn  H-infinity mixed-sensitivity design.
 ....
     
>> which mixsyn
/home/michael/MATLAB_2019b/toolbox/robust/robust/@DynamicSystem/mixsyn.m  % DynamicSystem method

According to ver, the toolbox is installed:

>> ver
-----------------------------------------------------------------------------------------------------
MATLAB Version: 9.7.0.1216025 (R2019b) Update 1
MATLAB License Number: XXXXXX
Operating System: Linux 5.0.0-32-generic #34~18.04.2-Ubuntu SMP Thu Oct 10 10:36:02 UTC 2019 x86_64
Java Version: Java 1.8.0_202-b08 with Oracle Corporation Java HotSpot(TM) 64-Bit Server VM mixed mode
-----------------------------------------------------------------------------------------------------
MATLAB                                                Version 9.7         (R2019b)
Simulink                                              Version 10.0        (R2019b)
Control System Toolbox                                Version 10.7        (R2019b)
Curve Fitting Toolbox                                 Version 3.5.10      (R2019b)
Model Predictive Control Toolbox                      Version 6.3.1       (R2019b)
Optimization Toolbox                                  Version 8.4         (R2019b)
Robust Control Toolbox                                Version 6.7         (R2019b)
Signal Processing Toolbox                             Version 8.3         (R2019b)
Statistics and Machine Learning Toolbox               Version 11.6        (R2019b)
Symbolic Math Toolbox                                 Version 8.4         (R2019b)

The license is also available, i.e.,

>> license('test', 'robust_toolbox')

ans =

     1

I have tried restarting MATLAB, resetting the matlab path, and rehash toolboxcache, but to no avail. There also are no variables or other functions shadowing the function; I also tried different functions from the toolbox, which did not work either.

I am gratefule for any advise on how to solve this problem.

Answer 1

[Pujitha Narra]

Hi Michael,

Can you run the following and let me know what errors you get.

openExample('robust/LoopShapingWithMixsynExample');

Answer 2

[Steven Lord]

There's no syntax listed on the documentation page for the mixsyn function that shows it being called with zero input arguments. The shortest syntax (in terms of number of inputs) lists four inputs. When you see ___ used in a syntax section, that can be replaced by any of the previous syntaxes. Therefore:

[K, CL, gamma, info] = mixsyn(G, W1, W2, W3, opts)

is an allowed syntax. In addition, as stated in the description of the G input argument the first input must be a dynamic system model (LTI) like one created by the ss function, the zpk function, etc.