Change diagonal place

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Paul
Paul 2011-12-22
How can I switch places the diagonal and the first column from a square matrix?
  1 个评论
Fangjun Jiang
Fangjun Jiang 2011-12-23
You could use an example to explain what you mean.

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采纳的回答

bym
bym 2011-12-23
a= magic(3)
a =
8 1 6
3 5 7
4 9 2
>> b=a;
>> for i =2:size(a,1)
b(i,1:i)= fliplr(a(i,1:i));
end
b
b =
8 1 6
5 3 7
2 9 4
  3 个评论
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Image Analyst
Image Analyst 2011-12-23
proecsm, I know you know better than that, so I assume you just made a careless error. See my solution for the correct answer. Paul, don't use that method if your size is greater than 3 by 3.
Andrei Bobrov
Andrei Bobrov 2011-12-23
b = 1:size(a,1)+1:numel(a)
c = 1:3
a([b,c]) = a([c,b])

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更多回答（1 个）

Image Analyst
Image Analyst 2011-12-23
This code works of a square matrix of any size. I present both a looping and vectorized way.
a=magic(6)
b=a;
for i =2:size(a,1)
temp = a(i,i);
b(i,i)= b(i,1);
b(i,1) = temp;
end
b
% Loopless way
a=magic(6)
b=a;
diagonalElementsMask = logical(eye(size(a,1)))
% Save diagonal elements, because we're going to replace them.
bDiagonalElements = b(diagonalElementsMask)
% Replace diagonal elements with first column.
b(diagonalElementsMask) = b(:,1);
% Replace first column with diagonal elements.
b(:,1) = bDiagonalElements
a =
35 1 6 26 19 24
3 32 7 21 23 25
31 9 2 22 27 20
8 28 33 17 10 15
30 5 34 12 14 16
4 36 29 13 18 11
b =
35 1 6 26 19 24
32 3 7 21 23 25
2 9 31 22 27 20
17 28 33 8 10 15
14 5 34 12 30 16
11 36 29 13 18 4
  3 个评论
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Andrei Bobrov
Andrei Bobrov 2011-12-23
b = 1:size(a,1)+1:numel(a)
c = 1:size(a,1)
a([b,c]) = a([c,b])
Image Analyst
Image Analyst 2011-12-23
OK, this one works.

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