max(A) is a vector, not a number:
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 1
2 2
3 3
4 4
5 5
6 6
7 7
8 8
9 9
10 10
11 11
12 12
13 13
14 14
15 15
16 16
17 18
18 18
19 19
