# How to find the index of any maximum matrix?

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vimal kumar chawda on 9 Jul 2021
Commented: DGM on 11 Jul 2021
I need the index or position in column and row of the maximum value.
X =rand(20)
How can I ?
##### 2 CommentsShowHide 1 older comment
Stephen23 on 11 Jul 2021
You might not use tags, but you are not the only user of this forum, and some of us certainly do use tags.

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.
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.

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.

R2021a

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