Index exceeds the number of array error

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Sashi Mendoza
Sashi Mendoza on 31 Mar 2022
Edited: Sashi Mendoza on 3 Apr 2022
a = a certain 20x20 matrix;
[val,idx] = max(a(:));
[x, y] = find(a == val);
At the underlined part of the code, this displays the error "Index exceeds the number of array elements (1)". How to fix this?
  3 Comments
Stephen23
Stephen23 on 31 Mar 2022
"x = 11 and y = 21 though"
And why do you expect that IDX should be able to index into scalar numerics?

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Accepted Answer

Arif Hoq
Arif Hoq on 31 Mar 2022
Edited: Arif Hoq on 31 Mar 2022
var = randi(100,20,20);
[val,idx] = max(var(:))
val = 100
idx = 15
[x, y] = find(var == val)
x = 7×1
15 5 15 14 16 7 14
y = 7×1
1 5 7 13 19 20 20
idx2=2;
x0 = x(idx2)
x0 = 5
y0 = y(idx2)
y0 = 5
here your idx=2(intentionally fixed) and your number of element of x and y is 7. so x0 and y0 can extract from index 2. now see the below example
%%
var = randi(100,20,20);
[val,idx] = max(var(:))
val = 100
idx = 18
[x, y] = find(var == val)
x = 5×1
18 16 7 4 10
y = 5×1
1 4 8 9 14
% idx2=2;
x0 = x(idx)
Index exceeds the number of array elements. Index must not exceed 5.
y0 = y(idx)
here your idx=18, but your number of element of x and y is 5.so it can not extract form index 18. therefore, you are getting error.
  2 Comments
Stephen23
Stephen23 on 31 Mar 2022
"Stephen said already you can not specify index in a sclar value"
It is certainly possible to index into a scalar value:
A = 6;
A(1,1)
ans = 6
But just like any other indexing, those indices must be within the size of that (scalar) array.... which IDX is not.

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