False Output from find-function?

max(A)
ans =
  Columns 1 through 15
    1.0000    1.0000    1.0000    1.0000    1.0000    1.0000    1.0000    1.0000    1.0000    1.0000    0.9999    1.0000    1.0000    1.0000    1.0000
  Columns 16 through 20
    1.0000    0.7950    1.0000    1.0000    0.9998

The value at A(19,17) is the 0.795, which is not a maximum of the matrix but rather a maximum of the column.

if you want to get the maximum of the whole matrix you need this:

max(A(:))
ans =
    1.0000

And when you compare, remember that float value comparison is everything but reliable, so you need to have a given tolerance.

In your code it would be something like this:

[rows, columns] = find( abs(A-max(A(:)))<1e-4  );
ans =
   1
   2
   3
   4
   5
   6
   7
   8
   9
  10
  11
  12
  13
  14
  15
  16
  18
  18
  19

3 个评论
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Rene 2020-8-31

I'm sorry but it did not work out like I wanted it.

I tried it with another matrix:

A = [1 0.5 0.7;0.4 0.8 0.4;0.2 0.3 0.7];

It only gave me the value 1.

I then created a loop to get the maximum of each row

k = 1;
for i = 1 : size(A,1)
    Max(k,1) = max(A(i,:));
    k = k+1;
end

This gives me the maximums I need in the right order.

1
0.8
0.7

Now I want the location too. Like so:

%row   col     value
1	1
2	0.8
3	0.7

I tried the find again but as soon as there are multiple of the same value in the matrix it wont work like this:

k = 1;
for i = 1 : size(A,1)
    Max(k,1) = max(A(i,:));
    [row,col] = find(A==max(A(i,:)));
    row(k,1) = row;
    col(k,1) = col;
    k = k+1;
end

Any idea how to get the column value of the exact max value I'm looking for?

Thiago Henrique Gomes Lobato 2020-9-2

This will probably work for you

A = [1 0.5 0.7;0.4 0.8 0.4;0.2 0.3 0.7];
Amax = max(A); % Get maximum from each column
DiffFromMax  = A-Amax; % Zero values are maximum locations
tol = -1e-4; % Note that the tolerance is negative
[rows, columns] = find( DiffFromMax>tol )

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