How to load an object of class 'sym' in a .mat file

Hello,

I have a .mat file which contains objects of class 'sym'. When I try to open this .mat file, MATLAB 2023a gives me the following error:

Warning: Cannot load an object of class 'sym': Its class cannot be found. 
Warning: Some variables failed to load, and have been replaced with empty arrays. This might have happened if their classes do not exist on the path. 

What should I do in this case to open this .mat file?

Answer 1

[Steven Lord]

Do you have Symbolic Math Toolbox installed? If you don't, you won't be able to load sym objects created with the sym or syms functions from that toolbox.

[Walter Roberson]

Note that in particular you will not be able to load such a file inside an executable created by MATLAB Compiler, as the Symbolic Toolbox cannot be compiled at all.

[Dyuman Joshi]

@Walter Roberson

"... as the Symbolic Toolbox cannot be compiled at all."

I am curious as to why is that? Was it written/programmed in that manner?

Also, do all of the other toolboxes behave similarly i.e. they can't be compiled as well?

[Steven Lord]

Also, do all of the other toolboxes behave similarly i.e. they can be compiled as well?

See the MATLAB Compiler and Simulink Compiler support page for a table of which functionality from each product is supported for use with MATLAB Compiler and Simulink Compiler.

[Dyuman Joshi]

Thanks for the info, @Steven Lord

[Walter Roberson]

@Dyuman Joshi

The Symbolic Toolbox computations are performed in a separate process by the Symbolic Engine (symengine). Management of that complete separate process would be needed in order to support compiling the Symbolic Toolbox facilities.

At the moment I do not know of any technical reason why it could not be done, even if it would be a bit clumsy to do it (for example it might mean that every MCR had to include a copy of the engine executable). There are sometimes things that are not especially convenient to do but are not especially "hard" to do.

I have long suspected that there might be licensing reasons involved. Mathworks bought the MuPAD symbolic engine from a company, but that also means that they own the technical rights, so I don't think that it is a limit imposed by an outside company.

However... it could plausibly have to do with the fact that the symbolic engine is a complete programming language, and the input to it is effectively "data" as far as MATLAB is concerned, so if the engine could be compiled, then a sufficiently determined person could create a user interface that allowed a .exe to make general user-specific computations (by routing them through the symbolic engine.) Mathworks is not fond of that possibility, I know.