Can you create an object in Simulink that can be referenced by multiple MATLAB Fcn blocks?

I've attached an image with my current Simulink set-up. I am needing to replace the Interpreted MATLAB Fcn blocks with MATLAB Fcn blocks in order to make my Simulink code generation compatible. However, I am struggling to find a way to mimick this similar OOP approach - where I am essentially creating a global object that is being referenced and manipulated by multiple blocks.

With the MATLAB Fcn block, it is only creating a local object for that specific block. It cannot be referenced and manipulated by another MATLAB Fcn block. I run into a similar issue when trying it with MATLAB System blocks. Is there a workaround for this to get this "global object" character?

[Umar]

Hi Roop,

To answer your question, you can achieve a similar effect by using persistent variables within the MATLAB Fcn blocks. By declaring a variable as persistent, its value persists across multiple calls to the block. This approach allows you to maintain state information similar to a global object.

[Roop]

I want to be able to have this variable and its value persist across multiple blocks, not just multiple calls to the same block. Is there any workaround for this?

[Umar]

Hi Roop,

Thanks for clarifying this issue, to maintain persistent variables across multiple Fcn blocks, you can utilize the set_param function to set the block's mask parameters. By setting the mask parameters of a block, you can effectively share variables among multiple blocks. This approach allows you to achieve persistence across various blocks in your Simulink model. Here is an example illustrating how to use set_param to maintain a persistent variable across multiple Fcn blocks:

% Set the mask parameter of the first block
set_param('model_name/Block1', 'MaskValueString', 'persistent_var=0;');
% Access the persistent variable in the second block
persistent_var = evalin('base', 'persistent_var');

By setting and accessing mask parameters using set_param and evalin, you can create a workaround to maintain persistent variables across multiple MATLAB Fcn blocks.

For more information on set_param and evalin functions, please refer to

https://www.mathworks.com/help/simulink/slref/set_param.html

https://www.mathworks.com/help/matlab/ref/evalin.html

Hope this should help resolve your problem.

[Roop]

I don't belive this method works for objects of user-defined classes. For instance, my object has properties that return variable size structs, App Designer UI's, and other complicated data types. Are there any addtional potential workarouds?

[Umar]

Hi @Roop,

To address your query regarding, “ I don't belive this method works for objects of user-defined classes. For instance, my object has properties that return variable size structs, App Designer UI's, and other complicated data types. Are there any addtional potential workarouds?”

I do understand that the set_param and evalin approach may not directly work for objects of user-defined classes with complex data types unless you utilize global variables within MATLAB because by declaring a variable as global within a function block, you can maintain its value across multiple function calls. Hope this helps.

Answer 1

[Paul]

Hi Roop,

If you want to use global data inside Matlab Function blocks, start from Use Global Data in MATLAB Function Blocks to assess if any of the provided methods are sufficient for your use-case.

I do not know if the Matlab Function blocks support use of user-defined classes (UDC) as seems to be the case here. Even if so, I'm not sure if a UDC instance can be used as a global object, and, frankly, I suspect that won't pe possible because this Simulink paradigm is based on Simulink.Signal objects. If it isn't there may be other workarounds.

[Roop]

Thanks for the resource! As you said, the implementation stated in that resource doesn't support user-defined classes of complex data types, such as structs, other objects, etc. It only supports objects of simple data types, such as double, int, etc. Any other workarounds you can think of?

[Paul]

I vaguely recall having an idea to pursue when this question was first posted a month ago, but I can't recall what it was. It was probably something along the lines of using your object in an ordinary function that's called from the Matlab Function and declared therein with coder.extrinsic. However, it sounds like you need to generate code for the entire project, which, I believe, is not feasible if calling an extrinsic function.

I guess any other workaround would depend on exaclty why you need that instance of a UDC and what you're doing with it during simulation. Maybe it's possible to extract data from the object pre-sim, use the data during sim, then load the data back into the object post-sim.

[Roop]

Hmm... yeah I think I might need to extract the particular data from my object that I am working with in Simulation. Unfortunately, my UDC is difficult to describe because proprietary work, but essentially I am intending to

• Grab the object's current paramter data
• Feed it into a S-Function (with MEX file) which is tied to an external model
• Set the object's parameter data to the results
• And continually iterate this process during the entire simulation time

Issue is maintaing the same instance of the object to read and write data to, which I was able to do with Interpreted Fcn blocks, but now that I need code generation compatibility, it is proving difficult to replace with MATLAB Fcn or MATLAB System blocks and get that same "global object" behavior.

[Paul]

Is there really a need to update the object during simulation?

Or do you just need to iterate on the data during simulation?