Doubt regarding max(A,B).
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A=[1 3 5]
B=[10 6 4]
Why is max(A,B) as [10 6 5]?
It should be [5 10]
回答（2 个）
"Why is max(A,B) as [10 6 5]?"
Because that syntax provides an element-wise comparison of the two input arrays, taking the maximum value from either one of the input arrays:
- the maximum of 1 and 10 is 10
- the maximum of 3 and 6 is 6
- the maximum of 5 and 4 is 5
"It should be [5 10]"
No, it should not be.
What are are expecting is the maximum of each row of one matrix (not comparing the elements of two different arrays):
max([A;B],[],2)
Note that in some other languages the two functionalities are considered as different functions, e.g. in numpy they are amax and maximum respectively.
1 个评论
I suspect the original poster's mental model may have been that max(A, B) is [max(A), max(B)] and max(A, B, C, ...) is the same as [max(A), max(B), max(C), ...]. But as many people have said in this discussion, that is incorrect. If A and B are the same size each element of the output of max(A, B) is the maximum of the corresponding elements of A and B.
A=[1 3 5];
B=[10 6 4];
C_allAtOnce = max(A, B)
C_oneAtATime = [max(A(1), B(1)), max(A(2), B(2)), max(A(3), B(3))]
Compare with:
maxOfEachVector = [max(A), max(B)]
VBBV
2021-8-21
1 个投票
%f true max([A B]) max([A;B])
The first would give 10 as max value. The second would give 10 6 5 as max values along each column
6 个评论
S Priya
2021-8-21
"max(A,B) By default max uses column as 1st dimension. So above usage also gives same result as 10 6 5"
This is incorrect.
Do NOT learn from this incorrect comment.
The default direction is only relevant when one input array only is provided (i.e. when the maximum is taken along any dimension of one array), not when comparing the elements of two arrays. With the syntax shown in the question, the default direction is totally irrelevant.
Even for just one input array the default direction is not the "column as 1st dimension", but is actually the first non-scalar dimension.
This explanation indicates a major confusion of how MAX and MIN syntaxes work.
VBBV
2021-8-21
read the doc page of max for more clarity
VBBV
2021-8-21
For the OP.
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2021-8-21
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