How to find positive and negative outputs?

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Emily 2022-5-9

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https://ww2.mathworks.cn/matlabcentral/answers/1715365-how-to-find-positive-and-negative-outputs

回答： Emily 2022-5-10

Hi, I'm trying to have a= dif<-100 or dif>100 with dif being the difference between two numbers, but having trouble getting the negative values to work.

I currently have it as

for i=0:5

dif=struct.smth(:,10) - struct.smth(:,i)

num = (dif <-100) | (100 < dif);

Set.Number =find(num);

end

I have also tried

dif=abs(dif);

num=100<dif;

Set.Number =find(num);

but still only get the positive values to work.

The output when the negative number is triggered is "0x1 empty double column vector"

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Voss 2022-5-10

@Emily Maybe there are no elements of dif less than -100.

Can you provide a concrete example where the output of find is not what you expect?

dpb 2022-5-10

编辑：dpb 2022-5-10

在 MATLAB Online 中打开

" negative number is triggered is "0x1 empty double column vector"

It's always possible there ARE no values such that struct.smth(:,10) - struct.smth(:,i) < -100 in which case the empty vector is the expected result.

You need to always remember to write your code when using find and other functions which have such variable-number of outputs where, in fact, one of the valid results is that the result is NIL.

Often placing such code within the try...catch portion and the fixup code for the empty case in the catch...end portion of a try, catch block construct is a slick way to deal with the issue. It may be that the catch block is empty; there's nothing to do in that case.

Also NB:

ixG100 = find(abs(struct.smth(:,10) - struct.smth(:,i)) >100);

will find both cases; you can determine which easily enough when processing the results might be another way to approach it.

I didn't look at all at what really trying to do; just generic comments...

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