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

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???

Answer 1

[Azzi Abdelmalek]

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

[Zaza]

thanks a lot Azzi

ןt was a bit tricky for me

[Walter Roberson]

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).

Answer 2

[Roger Stafford]

 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);

Answer 3

[Azzi Abdelmalek]

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))

[Zaza]

can i get this using for or while? because in HW i can use length and size fun. only

[Azzi Abdelmalek]

Yes you can, try for loop

[Zaza]

for i=1:length(a)

M(i,:) = a(i);

i get the 1st column of M but i can't manipulate M to get the correct form of M...

[Azzi Abdelmalek]

Use circshift function in the loop

[Zaza]

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]

I will give you a hint

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

Answer 4

[Walter Roberson]

You can look at the code for toeplitz.m

Answer 5

[Image Analyst]

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).

[Zaza]

i meant that i can use only "size" and "length" functions

and i forget to mention that this has to work on any size of given array...

[Image Analyst]

Did you also forget to mention that it is homework? Because I can think of no other reason why you would be prohibited from using any function at your disposal to get the job done. Add that tag to your post if it's homework. We won't just give you the answer to your homework outright, but may give hints.

[Zaza]

i did mention that

tips are welcome

[Image Analyst]

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.

Answer 6

[Sean de Wolski]

M = a(sortrows(bsxfun(@(x,y)mod(x+y,numel(a))+1,1:numel(a),(1:numel(a))')))