What can I write in a MATLAB function block in Simulink?

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Maria 2017-12-12

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评论： Birdman 2017-12-13

Hi I am working with Simulink. I wrote a function in Matlab that basically does a circular shift, and I wanted to put it into Simulink by using the MATLAB function block. The thing is that if I write

function y= shift_with0(u,s)
y = circshift(u,s);
y(1:s)=0;
end

no problem and everything is working. But, I wanted to allow as inputs also vectors, so I wrote this function

function y= shift_with0(u,s)
if isvector(s)
    pm=sign(s);
    inegatif = sum(pm(:)==-1);
    s = inegatif;
end
y = circshift(u,s);
y(1:s)=0;
end

In Matlab is working, but the Simulink block not. So, I assume that is the "if" part that Simulink does not accept. In general, could someone clarify for me what I can write/not write in a MATLAB function block? Thanks

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KL 2017-12-12

编辑：KL 2017-12-12

在 MATLAB Online 中打开

isvector should return 1, even if it had only one element. It actually helps you differentiate between a vector and a matrix. try

isvector([1 2 3])

and then

isvector(1)

always read the documentation: https://www.mathworks.com/help/matlab/ref/isvector.html

Also, I do not get what you mean by y(1:s)=0;.

Maria 2017-12-12

编辑：Maria 2017-12-12

在 MATLAB Online 中打开

You are right about the isvector. I modified it

function y= shift_with0(u,s)
[n,m] = size(s);
if n>1 || m>1
  pm=sign(s);
  inegatif = sum(pm(:)==-1);
  s = inegatif;
end
y = circshift(u,s);
y(1:s)=0;
end

With y(1:s)=0 I set the components before the "s" point to zero. It is because want to shift indeed, not really to circularly shift. I found this solution that suits me. In front of the values that have been shifted, I want zero. In Matlab I get what I actually want. But Simulink complains. I attach the file.

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采纳的回答

Birdman 2017-12-12

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shifting.mdl

Run the attached model and let me know the results.

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Maria 2017-12-13

Thank you. I think I understood now what I can expect when I work with constants.

Birdman 2017-12-13

You are welcome, Maria.

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KL 2017-12-12

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在 MATLAB Online 中打开

If s is a vector, I will just count the number of negative entries, and then shift the y by this amount

Shouldn't you be simply writing,

...
if numel(s)>1
    s = numel(s(s<0));
end
y = circshift(u,s);
...

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KL 2017-12-12

编辑：KL 2017-12-12

The difference between matlab and simulink is not only with the block based modelling but also its code generating abilities. The matlab-function block gives you the ability to do that and of course it comes with a restriction. This is why you use extrinsic command for some matlab functions inside simulink.

Unlike matlab, when you assign/reassign you have to mind certain things in simulink environment.

You can read more to understand why this happens. Documentation is the best place to learn how things work.

https://www.mathworks.com/help/simulink/slref/matlabfunction.html

https://www.mathworks.com/help/simulink/ug/when-you-can-reassign-variable-properties-for-c-c-code-generation.html

https://www.mathworks.com/help/simulink/ug/best-practices-for-defining-variables-for-c-c-code-generation.html

Maria 2017-12-12