Unrecognized function from Robust Control Toolbox

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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.

Answers (2)

Pujitha Narra
Pujitha Narra on 13 Nov 2019
Hi Michael,
Can you run the following and let me know what errors you get.
openExample('robust/LoopShapingWithMixsynExample');

Steven Lord
Steven Lord on 13 Nov 2019
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.

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