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

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Zaza
Zaza el 2 de En. de 2013
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???

Respuesta aceptada

Azzi Abdelmalek
Azzi Abdelmalek el 2 de En. de 2013
Editada: Azzi Abdelmalek el 2 de En. de 2013
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 comentarios
Zaza
Zaza el 2 de En. de 2013
thanks a lot Azzi
ןt was a bit tricky for me
Walter Roberson
Walter Roberson el 2 de En. de 2013
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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Más respuestas (5)

Roger Stafford
Roger Stafford el 2 de En. de 2013
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 el 2 de En. de 2013
Editada: Azzi Abdelmalek el 2 de En. de 2013
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))
  6 comentarios
Zaza
Zaza el 2 de En. de 2013
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
Azzi Abdelmalek el 2 de En. de 2013
I will give you a hint
a=[12 21 32]
b=a([2 3 1])

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Walter Roberson
Walter Roberson el 2 de En. de 2013
You can look at the code for toeplitz.m

Image Analyst
Image Analyst el 2 de En. de 2013
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).
  4 comentarios
Zaza
Zaza el 2 de En. de 2013
i did mention that
tips are welcome
Image Analyst
Image Analyst el 2 de En. de 2013
Editada: Image Analyst el 2 de En. de 2013
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 el 2 de En. de 2013
M = a(sortrows(bsxfun(@(x,y)mod(x+y,numel(a))+1,1:numel(a),(1:numel(a))')))

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