Unable to Unpack Variables from Python to MATLAB Function in Simulink Model

Hi everyone,

I'm beginner in Matlab and I'm working on a project where I need to replace a scalar control block for an induction motor in Simulink with my own control block written in Python. The Python function calculates three variables that I need to pass back to MATLAB Function block, and convert to vector.

However, I'm running into an issue where MATLAB seems to treat these variables as non-iterable and can't unpack them properly. Even though my Python function returns a tuple with the three variables, MATLAB can't seem to process them as intended.

Here’s a summary of the setup:

MATLAB Function:

function Vabc = Run_in_Python(fRef)
Vabc = zeros(3, 1);
coder.extrinsic('py.ControllerPython.calc');
result = cell(py.ControllerPython.calc(fRef));
Vabc = vertcat(result);
end

Error:

Python Error: TypeError: cannot unpack non-iterable int object Error in calc Error in 'InductionMachineScalar/Control/Scalar controller/MATLAB Function' (line 6)

Thanks in advance!

[Walter Roberson]

Side note:

result = cell(py.ControllerPython.calc(fRef));

Unless cell is a method of whatever is being returned by py.ControllerPython.calc(fRef), then cell() expects a list of one or more non-negative integers, and creates a cell array of the given size.

Vabc = vertcat(result);

vertcat() of a cell array gives you back the same cell array. vertcat() of a single parameter always gives back the same parameter. Perhaps you wanted

Vabc = vertcat(result{:});

[Arseny]

@Walter Roberson

Thank you,

but if I use:

Vabc = vertcat(result{:});

I get that error:

Error:Brace indexing is not supported for variables of this type.

Function 'Control/Scalar controller/MATLAB Function' (#25.182.191), line 8, column 20:

"result{:}"

Launch diagnostic report.

Error:Errors occurred during parsing of 'InductionMachineScalar/Control/Scalar controller/MATLAB Function'.

Error:Errors occurred during parsing of 'InductionMachineScalar/Control/Scalar controller/MATLAB Function'.

[Paul]

Can you run these commands

result = cell(py.ControllerPython.calc(fRef));
whos result

at the Matlab command prompt and copy the commands and the results back to here so we can see the type and size of result?

Answer 1

[Gautam]

Hello Arseny,

You can unpack the elements of the tuple into a vector by first converting it to “double” and then using the “vertcat” function on it. We’d want to convert to double as converting tuples to double allows you to leverage MATLAB's matrix operations and built-in functions without additional type handling.

Just replace the lines 4 and 5 of your code with

result = double(py.ControllerPython.calc(fRef)); 
Vabc = vertcat(result(:));