Can the filtfilt function be used in the simulink block matlab function?

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Brecht Vermeulen 2018-7-23

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https://ww2.mathworks.cn/matlabcentral/answers/411707-can-the-filtfilt-function-be-used-in-the-simulink-block-matlab-function

评论： Brecht Vermeulen 2018-7-23

noncausalfilter.zip

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Goodafternoon,

I wanted to use a non-causal filter on a array of datapoints in my Simulink model. Therefore I implemented the filtfilt function in a matlab function block. However, I get the following error:

Simulink does not have enough information to determine output sizes for this block. If you think the errors below are inaccurate, try specifying types for the block inputs and/or sizes for the block outputs.
Component:MATLAB Function | Category:Coder error
Index exceeds array bounds.
Function 'MATLAB Function' (#737.23.38), line 3, column 3:
"filtfilt(1,2,u)"
Launch diagnostic report.
Component:MATLAB Function | Category:Coder error

What could be the problem here? If I use 'filter' it seems to work fine. I included a simple model in the attachment.

Kind regards,

Brecht

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Ryan Takatsuka 2018-7-23

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It looks like a and b cannot have the same length in the Simulink filtfilt() call for some reason. If you design a filter where a and b are different lengths, it seems to run:

filtfilt([1,1], 2, u)

Brecht Vermeulen 2018-7-23

Hi Ryan,

Thank you, indeed, it seems to run with the length of b > a. No idea why this is a problem though. But at least it's a workaround. I'll design a filter of this shape.

Kr brecht

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