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Index for array max (or min) in Simulink without variable-size signal or MATLAB Function block

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Michael
Michael on 28 Sep 2017
Commented: Dick Benson on 5 Aug 2020 at 21:06
In Simulink I have a signal that is a 1-D array. I need to get the index associated with the first maximum (or minimum) value in the array. In MATLAB, that's simply this:
>> [val,idx] = max([2 3 6 8 4 7 8 4 5 6])
val =
8
idx =
4
where idx is the item I'm looking for.
Trying to do that in Simulink seems to be much less straightforward. The MinMax block does not offer an option to output the index of the first maximum value.
Coupling a MinMax with a Find Nonzero Elements blocks as in the suggestion on this page does do the trick, but it comes with the problem that the output of the find block is a variable-sized signal. I don't want it to be a variable sized signal; I just want the first index.
One could also use a MATLAB Function block and use the MATLAB min or max function as above, but MATLAB Function blocks take obnoxiously long to compile and often generate code with a lot of gunky overhead.
Is there not a simple, clean, cheap way to get the first max index?

  1 Comment

Michael
Michael on 3 Oct 2017
FYI to anyone who stumbles across this page...MathWorks staff saw this question and generated an enhancement request for the MinMax block on 2 OCT 2017. Even if that eventually gets added to base Simulink, it doesn't help me in the near term at all.

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Accepted Answer

Peter Anderson
Peter Anderson on 26 Apr 2018
I was looking at this sort of problem (for me it was find the first non-zero element) and came up with a solution that doesn't involve toolboxes, MATLAB function blocks or variable size signals. You can solve it with a for-iterator subsystem.
Your min/max case will be slightly different but will have very similar structure.

  3 Comments

Michael
Michael on 27 Apr 2018
I'm not sure why I didn't think of a solution like this, but I was able to implement something similar to what you have above that did the trick perfectly. Thanks!
In case it saves anyone else a few minutes, attached are both the min/max version that I needed as well as a slightly modified version of the find first non-zero in Peter's solution which I expect will be useful to me at some point.
Juan Ocampo
Juan Ocampo on 4 Dec 2018
Congratulations great solution, thank you very muck for shearing it, i was thinking for a solution to this problem for a while and your solution is perfect.

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More Answers (2)

sl
sl on 13 Feb 2019
Hi Michael,
The logic below will fulfill your need.
Capture.PNG

Marco
Marco on 3 Oct 2017
Hello Michael, you can try to use Maximum and Minimum block (DSP System Toolbox).
BR Marco

  1 Comment

Michael
Michael on 3 Oct 2017
Those blocks do look like they'll do the job. Unfortunately I don't have the DSP System Toolbox so it's not really a viable solution for me. It seems incredible that you can't get the capability I'm looking for without an inefficient workaround like a MATALB Function block or buying an extra toolbox, but that seems to be the case...

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