how can i get a matrix from an array like this:

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Zaza
Zaza 2013-1-2
Starting with
a = [12 21 32];
I would like to get this:
M = [12 21 32; 21 32 12; 32 12 21];
with size and length fun. only
Is it some kind of loop???

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Azzi Abdelmalek
Azzi Abdelmalek 2013-1-2
编辑：Azzi Abdelmalek 2013-1-2
a = [12 21 32 42];
n=length(a)
M=a
for k=1:n-1
c=a(1)
a(1:end-1)=a(2:end)
a(end)=c
M=[M;a]
end
  2 个评论
Zaza
Zaza 2013-1-2
thanks a lot Azzi
ןt was a bit tricky for me
Walter Roberson
Walter Roberson 2013-1-2
This does not satisfy your stated requirements, as assignment and subscripting and [] are all functions in MATLAB: in particular, those operations call upon subsasgn(), subsref(), and vertcat (and horzcat).

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更多回答（5 个）

Roger Stafford
Roger Stafford 2013-1-2
M = hankel(a,fliplr(a));
or if you can't use the 'hankel' function do this
n = length(a);
M = reshape(a(mod(floor(((n+1)*(0:n^2-1))/n),n)+1),n,n);
Azzi Abdelmalek
Azzi Abdelmalek 2013-1-2
编辑：Azzi Abdelmalek 2013-1-2
M=[a ;circshift(a,[0 -1]); circshift(a,[0 -2])]
%or more general
a=[12 21 32 42 52]
M=cell2mat(arrayfun(@(x) circshift(a,[0 -x]),(0:numel(a)-1)','un',0))
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Zaza
Zaza 2013-1-2
i can't use this fun.
but i can't do it with size and length only
oh i must take a deep breath and try later...

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Walter Roberson
Walter Roberson 2013-1-2
You can look at the code for toeplitz.m
Image Analyst
Image Analyst 2013-1-2
I don't know what "with size and length fun. only" means, but the simplest solution is
M = [a(1,1), a(1,2), a(1,3); a(1,2), a(1,3), a(1,1); a(1,3), a(1,1), a(1,2)];
Since you haven't given any other requirements, like it needs to work for other sizes of matrices, this will work exactly as you have said. No functions like toeplitz() or circshift() needed. If you needed other requirements and flexibility, I assume you would have said so (ok, that's probably a bad assumption given the types of posts people make).
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Image Analyst
Image Analyst 2013-1-2
编辑：Image Analyst 2013-1-2
OK - I didn't know the acronym HW. Others probably didn't recognize that as homework either, because it looks like three people have already done your homework for you and given you an answer that should work. I'll add the "homework" tag for you. Next time you can add it yourself so you won't be caught copying.

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Sean de Wolski
Sean de Wolski 2013-1-2
M = a(sortrows(bsxfun(@(x,y)mod(x+y,numel(a))+1,1:numel(a),(1:numel(a))')))

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