MATLAB: Are the MATLAB Function block arguments being inferred as variable size

simulink

Hi,

I am running into the following error message with a Simulink Model using a MATLAB Function Block.

Data 'out' 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.

It is not clear to me why the matrix is being inferred as variable size. Inside, the MATLAB Function Block, I define out to have a certain, fixed size corresponding to the values of two other parameters defined in the MATLAB Function block, as follows:

>> out = zeros(X,Y);

X and Y are defined as parameters within the MATLAB Function block, but they do not change during the simulation.

Why is the array variable-sized, and how do I resolve this??

Best Answer

In this particular case, variables X and Y were defined as Tunable parameters within the MATLAB Function block. This leads to Simulink interpreting the array as variable sized because X and Y could theoretically change during the simulation, even though their values clearly do not change here.

To resolve this, there are two potential solutions:

Set X and Y to be non-tunable using the 'Edit Data' option from within the MATLAB Function Block.
Set 'out' to variable-size as suggested by the message. In most cases this will resolve the warning straight away, but there may be other limitations that cause warnings/errors elsewhere in the model, so in general this should be recommended second.

Other users have encountered the same thing here:

https://www.mathworks.com/matlabcentral/answers/79239-error-due-to-variable-size-data-in-matlab-function-block

Related Solutions

MATLAB: Am I getting a computed maximum size is not bounded error in a MATLAB function block in Simulink R2018b

The reason for the error is that there is a dynamically sized array in the MATLAB Function Block that depends on a tunable input parameter. In the example the array "B" is equal to "ones(A)" where "A" is a tunable input parameter. Because "A" is unknown at compile-time, the size of "B" is also unknown at compile-time and thus we cannot statically allocate memory for "B". Even if we define a max size for "B" using "coder.varsize", there is no guarantee that "A" will be less than the maximum size for B, thus the error persists.

Here are three possible solutions to this problem:

1. If you do not need the parameter "A" to be tunable, then you can make "A" nontunable by un-checking the "Tunable" checkbox for A in the "Ports and Data Manager" (link below). Now we can check for the size of B at compile-time and the error is removed.

https://www.mathworks.com/help/simulink/ug/_bqgwvsq-1.html

2. You can also add an "assert" statement that can be used to enforce the max size of "B" and thus the B will be statically allocated at its maximum size. For example, add the following line to the MATLAB Function block code:

assert(A<10);

3. We can specify the variable sized arrays to be dynamically allocated, thus we do not need to know their size at compile-time because they will be set at run-time. We can do this by turning on "Dynamic Memory Allocation in MATLAB Functions" in the configuration parameters. Also by setting the "Dynamic Memory Allocation Threshold in MATLAB Functions" to "0", we can guarantee that all variable sized arrays will be dynamically allocated. See link for details:

https://www.mathworks.com/help/simulink/ug/use-dynamic-memory-allocation-for-variable-size-arrays-in-a-matlab-function-block.html

MATLAB: How to resolve an error about variable sized data in the MATLAB Function block

If the size of the variable can change during run-time:

You need to set up the sizes in the Data Editor for the MATLAB Function Block as per:

http://www.mathworks.com/help/simulink/ug/declare-variable-size-inputs-and-outputs.html

In the editor for your MATLAB Function Block code, click "Edit Data" to open the Ports and Data Manager, and check the variable-size box for y and give, for example, [513 1] as the upper bound/size. Doing this alerts Simulink to the fact that the data should be variable-size.

If the size of the variable does not change during run-time:

In case you do not want to have variable-size signals in your model, and the size of your data does not change during run-time and is known at compile-time, consider the following approach:

Define a parameter for your MATLAB Function Block by clicking Add > Data in the Ports and Data Manager. Select 'Parameter' as scope, and make sure that the 'Tunable' box is not checked.

You can use this constant parameter now to define the variable sizes at compile-time, by creating a variable of the same name in the MATLAB or model workspace or in the workspace of a masked subsystem containing this MATLAB Function Block. Then, you will be able to use code such as the following in your MATLAB Function block:

>> out = zeros(small,1);

This approach is also outlined in the following post:https://www.mathworks.com/matlabcentral/answers/513980-why-are-my-matlab-function-block-arguments-being-inferred-as-variable-size

Best Answer

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MATLAB: Am I getting a computed maximum size is not bounded error in a MATLAB function block in Simulink R2018b

MATLAB: How to resolve an error about variable sized data in the MATLAB Function block

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