MATLAB: Return values of function vs. assignin

assigninfunctionMATLABsimulink

Hi,

I'm writing a MATLAB function that sets some variables for a Simulink simulation of a planar robot.

A bunch of values are to be set in the workspace, around 20. However, about half of them should be of no interest for the end user, because they are internal variables of the simulation (variables for Simulink switches, for handling errors in the simulation, etc.). Also, they have to be saved in the workspace with the name that's used in the Simulink model.

Because of this, I was thinking about storing these values not by return values of the function, but by using the assignin function. This way, they could be stored with the right names in the workspace and the end user could ignore them.

Do you think it would be appropriate or just confusing and smell of bad design?

Thank you.

Best Answer

I understand that you wish to set some parameters in the workspace before you execute your model but don’t wish the end user to do it every time. I suggest you use Callbacks instead of a function. You may refer to the following documentation for more information about callbacks-

https://www.mathworks.com/help/simulink/ug/model-callbacks.html#btoznm0

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MATLAB: Access variables in several .mat files

Here is a simpler, faster method, without using slow and buggy eval:

files = {'file1.mat', 'file2.mat', 'file3.mat', 'file4.mat'};
S = load(files{1});
for m = 2:numel(files)
    S(m,1) = load(files{m});
end
C = struct2cell(S)';

and it gives exactly the cell array requested in the original question:

>> size(C)
ans =
     4    20
>> size(C{1,1})
ans =
           1      160000

This code assumes that the only fields in the mat files are those that are required. If there are other fields in the mat files, simply specify the required fields in the load call:

names = arrayfun(@(n)sprintf('RW_%02d',n),1:20,'Uni',false);
S = load(files{1},names{:});
etc.

Tip for beginners: rather than fighting MATLAB by using eval and other buggy, slow, and obfuscated commands, learn how to use MATLAB effectively by understanding matrices, arrays, and indexing:

https://www.mathworks.com/matlabcentral/answers/228557-experts-of-matlab-how-did-you-learn-any-advice-for-beginner-intermediate-users

A discussion of why eval is not the solution that beginners imagine it to be:

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

https://www.mathworks.com/matlabcentral/answers/196952-how-to-create-new-variables-in-batches-with-strcat

MATLAB: How to warn users that a simulation was run using the ‘sim’ function vs the GUI play button

To warn when 'sim' is used to run the simulation, please add 'disp' to the callback.

Add something like the following in StopFcn callback.

>> disp("Warning: if you see this warning in Command Window, please use the wrapper");

Because 'disp' is displayed on Command Window only when 'sim' is used to run the simulation, it is a good way to warn users.

https://www.mathworks.com/matlabcentral/answers/469921-why-do-fprintf-and-disp-not-show-in-the-command-window-when-called-from-simulink-callbacks-why

Best Answer

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