Matlab can not evaluate the maximum of an array?

Question

Alessandro Longo 2017-11-8

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回答： Steven Lord 2017-11-8

Hello, I am trying this simple Simulink diagram:

and I would calculate the maximum of the function (that is 1). As you can see, it does not work. Just for completion, this is the Matlab function code:

 function y = fcn(u)
 y = max(u);

Why?

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Birdman 2017-11-8

I can't open it with r2017a, please export it to r2017a.

Alessandro Longo 2017-11-8

编辑：Alessandro Longo 2017-11-8

Try this link, I can not update slx files Download

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Answer 1

Rik 2017-11-8

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在 MATLAB Online 中打开

I have hardly ever worked with Simulink, so I might be wrong, but I would think the function gets executed every time step (which would explain the almost 0 value). So you will have to define a persistent variable in your function to save the previous maximum.

function y=fcn(u)
persistent OldMaximum
if isempty(OldMaximum),OldMaximum=-if;end
OldMaximum=max([OldMaximum u]);
y=OldMaximum;%persistent variables can't be used as an output

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Alessandro Longo 2017-11-8

I tried to paste your code but Simulink tells me there is an error in the if block (Illegal use of if)

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Answer 2

Steven Lord 2017-11-8

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What is the maximum of your signal at time t = 2? Since your signal is a scalar the maximum of a scalar is the scalar itself. Since it sounds like you want the maximum over time not the maximum over the elements in your signal use the MinMax Running Resettable block instead of the MATLAB Function block or the MinMax block.