# How to read elements of a matrix diagonally in MATLAB?

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Febin Benjamin il 18 Set 2013
Suppose A is a 3X3 matrix
A=[2,5,7; 3,0,1; 9,17,23]
I want to read the elements in this fashion.
2
5 3
9 0 7
1 17
23
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### Risposta accettata

Andrei Bobrov il 18 Set 2013
Modificato: Andrei Bobrov il 18 Set 2013
A=[2,5,7; 3,0,1; 9,17,23]
k = spdiags(rot90(A));
s = size(k);
nns = nan(s);
ptr = tril(triu(ones(s)),s(1)-1);
nns(ptr>0) = k(ptr>0);
nns(:,1:2:end) = nns(end:-1:1,1:2:end);
out = sort(ptr,'descend');
out(out>0) = nns(~isnan(nns));
out = out';
or
A=[2,5,7; 3,0,1; 9,17,23];
ds = spdiags(rot90(A));
l = spdiags(ones(size(A)));
ds(:,1:2:end) = flipud(ds(:,1:2:end));
l(:,1:2:end) = flipud(l(:,1:2:end));
l2 = sort(l,'descend');
l2(l2>0) = ds(l>0);
out = l2';
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Febin Benjamin il 18 Set 2013
@Jan: I tried hard to frame the question in a comprehensive way but that's what I managed to come up with. :) Fortunately, Andrei got it! hehe :)
Andrei Bobrov il 18 Set 2013
B = [2,5,7; 3,0,1; 9,17,23];
A = fliplr(B); % and etc

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