How to repeat a rectangular matrix in matlab?

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rui
rui 2014-7-24
评论： rui 2014-7-25
How to repeat a rectangular matrix in matlab?
Not using loops, just matlab's build-in commands.
Thanks a lot!

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Star Strider
Star Strider 2014-7-24
编辑：Star Strider 2014-7-24
This works:
a = [1 1 1 1; 2 2 2 2];
A = zeros(6);
for k1 = 1:2:size(A,1)-1
A(k1:k1+1, k1:k1+3) = a;
end
A % Show Result
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rui
rui 2014-7-24
I used circshift, sparse and loops in my code but it still takes a very long time to obtain the results, and I've been searching all day but with no luck, so I guess that loop is inevitable in this situation. Thank you so much for your help, I really appreciate it!
Star Strider
Star Strider 2014-7-24
My pleasure!
The circshift approach (that I used) expands the matrix with each step. That takes more time, because MATLAB has to allocate new memory each time.
I suggest using my first approach and preallocating the matrix. That eliminates the problem of expanding the matrix at each step, eliminates the call to circshift, and produces the same result.

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Azzi Abdelmalek
Azzi Abdelmalek 2014-7-24
编辑：Azzi Abdelmalek 2014-7-24
A=[1 2 ; 3 4]
B=repmat(A,3,2)
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Azzi Abdelmalek
Azzi Abdelmalek 2014-7-24
You didn't say anything about how do you want to shift your matrix? it's not just repeating a matrix.
rui
rui 2014-7-24
My mistake. Shifting the matrix by 2 positions in 2-dimensions. At the beginning there is a=[1 1 1 1;2 2 2 2], after doing it 3 times without using any loops (just using build-in commands), it becomes a 6-by-8 matrix as shown in the picture. Those extra positions are filled by 0s automatically. Thanks again.

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Andrei Bobrov
Andrei Bobrov 2014-7-24
编辑：Andrei Bobrov 2014-7-24
for your case:
t = zeros(6,2);
out = [kron(eye(3),a(:,1:2)),t]+[t,kron(eye(3),a(:,3:4))];
variant
m = 3;
k=2;
s = size(a);
n = (m-1)*k+s(2);
m1 = m*s(1);
out = zeros(m1,n);
t = sub2ind([m1,n],1:s(1):m1,1:k:k*m);
t2 = bsxfun(@plus,(0:s(2)-1)*m1,(0:s(1)-1)');
out(bsxfun(@plus,t,t2(:))) = a(:,:,ones(m,1));

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