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

Question

Zaza 2013-1-2

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https://ww2.mathworks.cn/matlabcentral/answers/57801-how-can-i-get-a-matrix-from-an-array-like-this

采纳的回答： Azzi Abdelmalek

在 MATLAB Online 中打开

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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Answer 1

Azzi Abdelmalek 2013-1-2

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编辑：Azzi Abdelmalek 2013-1-2

在 MATLAB Online 中打开

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

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Zaza 2013-1-2

thanks a lot Azzi

ןt was a bit tricky for me

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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Answer 2

Roger Stafford 2013-1-2

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在 MATLAB Online 中打开

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);

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Answer 3

Azzi Abdelmalek 2013-1-2

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编辑：Azzi Abdelmalek 2013-1-2

在 MATLAB Online 中打开

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 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...

Azzi Abdelmalek 2013-1-2

在 MATLAB Online 中打开

I will give you a hint

a=[12 21 32]
b=a([2 3 1])

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Answer 4

Walter Roberson 2013-1-2

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You can look at the code for toeplitz.m

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Answer 5

Image Analyst 2013-1-2

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在 MATLAB Online 中打开

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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Zaza 2013-1-2

i did mention that

tips are welcome

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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