Arrays and embedded MATLAB function in Simulink

Question

Floriane 2012-1-12

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回答： Abdulrahman Talib 2017-11-19

Dear all,

I am using Simulink (Matlab R2010a) to simulate the behaviour of an energy system. In this system, m boxes are connected in parallel and can be disconnected with a switch. The number of boxes m is a mask parameter which is defined by the user at the beginning of the simulation. Inputs of my embedded MATLAB function are the number of boxes m, the inlet power P[1,m] and the temperature T[1,m] of each box. Calculated parameters (outputs) are the produced gas flow rate G[1,m] and the temperature variation dT[1,m] of each box. The output dT[1,m] is connected with an integrator, which is connected with the input T[1,m].

This is the code structure in the embedded MATLAB function:

 function [G,dT] = Boxes(m,P,T)
G=zeros(1,m);
dT=zeros(1,m);
  for i=1:
  Pin=P(1,i);
  Tout=T(1,i);
  Gas=f(Pin,Tout);
  dTout=h(Pin,Tout);
  G(1,i)=Gas;
  dT(1,i)=dTout;
  end
end

This code works in Matlab, but the simulation does not work in Simulink. I get the following error message:

 Data 'dT' (#146) is inferred as a variable size matrix, while its specified type is something else.

In other words, I should specify in the "Ports and Data Manager" that the parameters P, T, G and dT are variable size matrix. But this would be wrong because the size of these arrays actually does not change during the simulation!

Another point: If I do so and specify that they are variable size matrix, I get the following error messages:

 Simulink cannot propagate the dimension mode from the output port 1 of 'Boxes/Bus Creator' to the input port 1 of 'Boxes/Memory'. One of the multiplexed signals at the output of the source has variable-size mode. This multiplexed signal has to be demultiplexed before Simulink can propagate it to the destination.

and

 Output 'dT' (#166) has variable size but the upper bound is not specified; explicit upper bound must be provided.

So I cannot use the Memory block with a variable size matrix and I have to explicit the upper bound of each variable size parameter.

Maybe I should explicit that these arrays are fixed size matrix, but I don’t know how.

Many thanks in advance for your help!

Floriane

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Kaustubha Govind 2014-7-10

Shruthi: You can configure that on the Ports and Data Manager in the right pane after selecting the corresponding parameter on the left pane.

Shruthi Kubatur 2014-7-21

Hi,

Thank you for your answer. I had a follow-up question. Let's say I have a struct that is being called (as a parameter) by an S-function block. How do I update (or change) certain fields of the struct inside the simulink block and have a copy of the struct written to matlab workspace?

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Answer 1

Mike Hosea 2012-1-18

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在 MATLAB Online 中打开

All signal inputs to an Embedded MATLAB Function block are inherently variable, even if they are emitted from a constant block. Why are you passing m in? I think you have a couple of options here. Either make it a non-tunable parameter or remove the input altogether and make

m = size(P,2);

the first line of code of the function. Or perhaps

G=zeros(size(P));
dT=zeros(size(T));

would be correct. Anyway, the point is that to the extent possible, you should infer sizes from sizes, or make it a non-tunable parameter. -- Mike

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Answer 2

jabbar kamali 2013-8-10

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hello Mike Hosea! are u sure u have understood the questions? what u have said is compelletly unrelated to the issue!!!!!!!!!!!!

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Kaustubha Govind 2013-8-12

jabbar: Please post follow-up questions as a comment on the original question, and not as a new answer. Mike's answer does indeed address your question precisely, but perhaps you need some more context to understand it.

First of all - what is the variable 'm' in your block? Is it an input or a parameter? If it is an input, you're saying that the size of the outputs G and dT vary with the input signal - since they are defined as zeros(1,m). Perhaps you meant for 'm' to be a non-tunable parameter? Marking it as a non-tunable parameter means that it's value does not change during simulation, so none of the signals will be variable-size.

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