# How to mirror matrix on the diagonal?

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SL il 21 Ott 2016
Modificato: DGM il 3 Ago 2022
I want to mirror data matrix on the diagonal.
Input:
y
|
____ x
Expected output:
x
|_y
I know you these transformations but I cannot get mirror around the diagonal (y=x line from (0,0) to (1,1))
I2 = flipdim(I ,2); %# horizontal flip
I3 = flipdim(I ,1); %# vertical flip
I4 = flipdim(I3,2); %# horizontal+vertical flip
MATLAB: 2016b OS: Debian 8.5
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Massimo Zanetti il 21 Ott 2016
Can you give a simple example with numeric array of the "mirroring" you need? Is it something like:
1 2 3
4 5 6
7 8 9
to
9 6 3
8 5 2
7 4 1
?
SL il 21 Ott 2016

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### Risposta accettata

Thorsten il 21 Ott 2016
I2 = rot90(fliplr(I),-1);
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Yes. This works on n-d arrays. The other answers involving transpose do not work in arrays greater than 2 dimensions, unless you want to iterate thru the other dimensions.
DGM il 3 Ago 2022
To add to the confusion, depending on what version you use, this may still not work with arrays that are more than 2D. In older versions, rot90(), fliplr() and flipud() are limited to work only on 2D arrays. It might not be that relevant today, but this is not a current thread.

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### Più risposte (2)

Massimo Zanetti il 21 Ott 2016
Modificato: Massimo Zanetti il 21 Ott 2016
In the case described before it is:
A=[1 2 3;4 5 6;7 8 9]
rot90(A,2)'
which gives:
A= 1 2 3
4 5 6
7 8 9
to
9 6 3
8 5 2
7 4 1
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Massimo Zanetti il 22 Ott 2016
I can't see why it shouldn't work... You must give me an example, otherwise I cannot understand. No problems with rectangular matrices.
DGM il 3 Ago 2022
Modificato: DGM il 3 Ago 2022
The transpose operator doesn't work on anything other than a 2D array, but you can still use permute().
A = repmat([1 2 3;4 5 6;7 8 9],[1 1 3])
A =
A(:,:,1) = 1 2 3 4 5 6 7 8 9 A(:,:,2) = 1 2 3 4 5 6 7 8 9 A(:,:,3) = 1 2 3 4 5 6 7 8 9
B = permute(rot90(A,2),[2 1 3]) % use permute()
B =
B(:,:,1) = 9 6 3 8 5 2 7 4 1 B(:,:,2) = 9 6 3 8 5 2 7 4 1 B(:,:,3) = 9 6 3 8 5 2 7 4 1
C = pagetranspose(rot90(A,2)) % or use pagetranspose() (R2020b or newer)
C =
C(:,:,1) = 9 6 3 8 5 2 7 4 1 C(:,:,2) = 9 6 3 8 5 2 7 4 1 C(:,:,3) = 9 6 3 8 5 2 7 4 1
That said, if the OP isn't aware of the array dimensionality, then there are probably other problems.

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Fady Samann il 13 Ago 2020
you can do the following:
first, transpose the matrix
A = table.';
Flip it horizontally
A = flip (A,1);
then, flip it verticaly
A = flip (A,2);
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