Scalar variable as output of Matlab function in Simulink

Question

Rui Zhang 2023-2-16

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1913760-scalar-variable-as-output-of-matlab-function-in-simulink

评论： Fangjun Jiang 2023-2-16

I careted a Simulink model in MATLAB 2017 for debug. The model includes only a MATLAB function. It is shown in the image below;

The code in the MATLAB function looks like below:

function y = fcn(time,stateVariables)

ii = find(stateVariables(:,1)<=time,1,'last');

if isempty(ii)

ii = 1;

end

y = ii

end

The stateVariables was loaded in the base workspace, as a parameter of the function. The first column is the time.

stateVarables = [0 10;

1 20;

2 40;

3 50;];

When run the Simulink model, it showed the following error: " Data 'y' is inferred as a variable size matrix, while its properties in the Model Explorer specify its size as inherited or fixed. Please check the 'Variable Size' check box and specify the upper bounds in the size field."

Then I checked "Variable Size" box and put 1 in "Size" textbox. I got another error: "Size computation for 'y' (#831) failed. MATLAB Function Block and Stateflow do not support Variable Sizes for scalar signals."

Then I unchecked "Variable Size" box, and reset -1 in "Size textbox". Then I changed the code as following:

function y = fcn(time,stateVariables)

ii = find(stateVariables(:,1)<=time,1,'last');

if isempty(ii)

ii = 1;

end

y = reshape([ii 0],[2,1]);

end

And it works. But this is not what I want. In this case, I have to add additional column to the output.

My question is: how to get a scalar variable as output of the MATLAB function?

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Answer 1

Fangjun Jiang 2023-2-16

0
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1913760-scalar-variable-as-output-of-matlab-function-in-simulink#answer_1173260

编辑：Fangjun Jiang 2023-2-16

In your code, you use the find() function. It could return zero, one or more results. That is why the inital error message says "Data 'y' is inferred as a variable size matrix". The error that followed is caused by the "not-so-good-workaround" solution.

Even though you had the find(...,1,'last') option and further if-statement to guarantee the output y is a scalar, I guess MATLAB is not "smart" enough to recognize this. You could contact Mathworks tech support to see what they say about this.

A good workaround I have proved to work is this. Set everything back to the orignal default, add a line "ii=ii(1);" before the "y=ii;" line. It runs without any error.

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Rui Zhang 2023-2-16

Thank you for your answer!

I followed your recommendation and modified the code as following:

function y = fcn(time,stateVariables)

ii = find(stateVariables(:,1)<=time,1,'last');

if isempty(ii)

ii = 1;

end

% y = reshape([ii 0],[2,1]);

y = ii(1);

end

It works!

Just be curious. Before I posted my issue, I modified the output variable name shown as the following:

function ii = fcn(time,stateVariables)

ii = find(stateVariables(:,1)<=time,1,'last');

if isempty(ii)

ii = 1;

end

% y = reshape([ii 0],[2,1]);

ii = ii(1);

end

An error came out "

Data 'ii' is inferred as a variable size matrix, while its properties in the Model Explorer specify its size as inherited or fixed. Please check the 'Variable Size' check box and specify the upper bounds in the size field."

I didn't realize that changing the output variable name could solve the problem!