Unrecognized function or variable when calling a LinearModel from a Simulink Interpreted Function block

I have a Simulink block that previously called a "Scattered Interpolant" function with 3 inputs using a Interpreted Function block in 2021a. I have added that function to the "base" workspace with the assignin command from Matlab. But when I replaced the "Scattered Interpolant" with a "LinearModel" with 5 inputs (created with fitlm and also added to the "base" workspace memory), I now get the errors:

An error occurred while running the simulation and the simulation was terminated

Caused by:

• Error due to multiple causes.
• Unrecognized function or variable 'TB3_C'.
• Error in 'flow [kg//s]' while evaluating expression.

I presume that fitlm models are available to Simulink? What else could I have done wrong?

[Jon]

Please attach or cut and paste your code

[Dave Hall]

In the script that I call the Simulink model from, I load the LinearModel and then assign it to the 'base' workspace:

assignin('base','TB3_C',TB3_C);

I then call it from the Interpreted Function call using feval:

Ultimately, I'll pass the parameters for the function call, but for now, the constants [0,0,7,0,0,0] return the correct value with no error when I run feval from the workspace.

Answer 1

[Jon]

When I make an example following the steps you provide it runs without errors. Please attach your script, and Simulink model.

If you create or load TB3_C using a script (rather than a function) then I think it will already be in the base workspace, so the assignin seems redundant.

By the way, you can also use TB3_C.predict([0,0,7,0,0,0]) inside of your interpreted MATLAB function block rather than feval

[Dave Hall]

Actually, I was running from a function, not the workspace, but if I run it from the workspace, I get the same error. First, when I just call the function from that workspace, I get:

>> TB3_C.predict([0,0,7,0,0,0])

ans =

160.3801

However, when I run the Simulink program from the Matlab workspace, I get this error:

Error due to multiple causes.

Caused by:

Unable to resolve the TB3_C.predict.

Error in 'flow [kg//s]' while evaluating expression.

It really seems that the Simulink component can't see TB3_C.

[Dave Hall]

Interestingly, if I replace the fitlm LinearModel call (TB3_C.predict) with a scattered interpolant function call, it runs well. Is it perhaps a problem with my fitlm linear model? It was also created with 2021a, but on a different computer, with perhaps a different release.

[Jon]

I doubt that it is a problem with your fitlm linear model, as the error message, "Unrecognized function or variable 'TB3_C' " simply indicates that the object is not found in the current workspace. So I would suspect there is a typo somewhere, or the TB3_C is not in the .mat file you are loading from. I could try to help you debug it further if you provide a complete (so I can run it on my machine) runnable example (script, datafile(s), Simulink model file) that reproduces the problem.

[Dave Hall]

Unfortunately, I can't post my model, so I thought I'd create an example that illustrated the problem. Go figure, my simple example works fine. But knowing that this should work and with the tips you've given me, hopefully, I can uncover my error. Thanks for the help, and if I have related questions as I continue to work through this, I'll post here.

[Jon]

I would start by looking in your Workspace browser (tab on desktop) checking whether TB3_C is even there. I don't think it will be, because the error message is telling you the variable doesn't exist. Then try to just load the .mat file (I'm assuming from what you said that TB3_C is supposed to be in a .mat file) that you think has TB3_C in it and see if it is in the workspace. You can also right click on the .mat file and choose show details to see what is in the file, maybe TB3_C isn't even in there. Otherwise, most likely you have a small typo, for example a lower case where it should be capitalized in an assignment statement so perhaps you have an object called Tb3_C or TB3_c

[Dave Hall]

Very strange, but I found the problem. The function call was under a subsystem with a load statement in the Initialization tab of the mask to call a previous, differently named .mat file with different functions. When I deleted that load statement, everything runs as it should. I verified that this is the case. I genuinely don't understand why this would be, though, but I'm out of the woods.