how do i find argmax?

how do i find argmax of, say x=[1 2] without any user defined function?

Answer 1

[Walter Roberson]

 [argvalue, argmin] = min(x);
 [argvalue, argmax] = max(x);

[shikhar]

thanks a lot Mr.Roberson

Answer 2

[Lukasz Laszko]

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

[Walter Roberson]

@Shurum Salehkia

is Q1T a function? You have Q1T(0) which would not work if Q1T were a variable being indexed.

[James Tursa]

@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:

https://en.wikipedia.org/wiki/Arg_max

https://numpy.org/doc/stable/reference/generated/numpy.argmax.html

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]

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.

Answer 3

[Konstantin]

Great!!!!