how do i find argmax?

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shikhar
shikhar on 21 May 2013
Edited: James Tursa on 18 May 2021
how do i find argmax of, say x=[1 2] without any user defined function?

Accepted Answer

Walter Roberson
Walter Roberson on 21 May 2013
[argvalue, argmin] = min(x);
[argvalue, argmax] = max(x);
  1 Comment
shikhar
shikhar on 21 May 2013
Edited: shikhar on 21 May 2013
thanks a lot Mr.Roberson

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More Answers (2)

Lukasz Laszko
Lukasz Laszko on 28 Oct 2019
Edited: Lukasz Laszko on 28 Oct 2019
I'm afraid the answer by Walter Roberson is not correct. According to docs the second returned value contains indices of the minimum/maximum values of x. So to find argmax, you need to call x(max_ind),
eg.
x=0.1:.01:4*pi;
[max_val max_ind]=max(cos(x))
argmax=x(max_ind)
-->> max_val=1
-->> argmax=2pi
-->> max_ind=619
  3 Comments
James Tursa
James Tursa on 17 May 2021
Edited: James Tursa on 18 May 2021
@Lukasz Laszko Argmax is defined as the elements of the domain (i.e., in this case the indexes) where the function (i.e., in this case the vector) obtains the maximum. See these definitions:
Walter's answer is correct according to these definitions.
Your use of cos(x) introduces another function inbetween that was not part of the original question. Did the original question have cos(x) that was subsequently edited out?
Walter Roberson
Walter Roberson on 18 May 2021
In the case a function that is effectively f(x(K)) and what you wanted was the x(K) then it would not be unreasonable to take
fx = f(x);
[~, argidx] = max(fx);
argmax = x(argidx);
This adds an extra level of indirection, but it would be a common one.

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Konstantin
Konstantin on 12 Jun 2018
Great!!!!

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