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How to find the index of any maximum matrix?

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I have matrix X=radn(20)
I need the index or position in column and row of the maximum value.
X =rand(20)
How can I ?
  2 Comments
Image Analyst
Image Analyst on 11 Jul 2021
Wow, 107 tags, if I conted correctly. I think that must be a reconrd. It must have taken you more time to enter all those than to just look up max() in the help. I'll show you how to do it in my answer below.
Stephen23
Stephen23 on 11 Jul 2021
@vimal kumar chawda: please do not add 107 completely unrelated tags to your questions.
You might not use tags, but you are not the only user of this forum, and some of us certainly do use tags.

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Accepted Answer

DGM
DGM on 9 Jul 2021
Edited: DGM on 9 Jul 2021
s = [10 10];
x = randi(100,s)
x = 10×10
40 81 9 67 90 11 44 79 79 56 2 53 68 82 7 42 35 39 51 95 60 22 51 18 47 6 44 83 38 49 57 44 87 24 6 41 59 83 53 94 74 54 17 10 43 2 72 27 16 46 18 60 91 20 13 24 77 38 9 21 22 8 47 100 70 7 42 88 27 17 79 69 38 11 59 80 79 89 68 10 92 92 77 89 49 64 98 97 74 61 50 69 93 52 28 43 4 61 15 96
[~,idx] = max(x(:)) % this gets the linear index
idx = 37
[row col] = ind2sub(s,idx) % if you want subscripts instead
row = 7
col = 4
Of course, that's only the first instance of the maximal value.
  4 Comments
Image Analyst
Image Analyst on 11 Jul 2021
Actually since his question used randn() which will give unique floating point values and only one max value, not several, your suggestion to use max() is fine.
DGM
DGM on 11 Jul 2021
I just used randi so that the matrix was easier to read by eye and fit better on the page. The fact that it allows for frequent duplicates was what prompted me to mention the behavior.

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More Answers (1)

Image Analyst
Image Analyst on 11 Jul 2021
m = randi(9, 5, 5)
maxValue = max(m(:))
% Find out what rows and columns the max occurs in.
% Works even if the max occurs in more than one place
% unlike the index the second output argument of max() gives you.
[rowsOfMax, columnsOfMax] = find(m == maxValue)
You'll see:
m =
3 5 7 9 8
7 9 3 5 3
6 4 5 2 8
2 6 7 2 3
2 3 9 3 9
maxValue =
9
rowsOfMax =
2
5
1
5
columnsOfMax =
2
3
4
5
Like I said, it's a more robust solution than using max() alone.

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