Repmat with pattern
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Does anyone know an efficient way of replicating a matrix in a predetermined pattern(such as diagonal or triangular)?
Some examples: 1. We have A=[1,2;3,4] and we want B=[A,zeros(2);zeros(2),A] 2. We have A=[1,2;3,4] and we want B=[A,zeros(2);A,A] 3. We have a=[1;2;3;4] and we want B=[a,zeros(4,1);zeros(4,1),a]
采纳的回答
Walter Roberson
2012-1-20
3 个投票
- kron([1 0;0 1],A)
- kron([1 0;1 0],A)
- kron([1 0 0;0 0 1],A)
That is, put a 1 for each copy of A that should appear, and put a 0 for each place 0's the same size as A should appear.
6 个评论
Andrew Newell
2012-1-21
Wow! I wish I could vote for this one twice!
Andrew Newell
2012-1-21
However, I think 2 and 3 should be
kron([1 0; 1 1],A)
kron([1 0; 1 0],A)
Mohammad Tabesh
2012-1-21
Walter Roberson
2012-1-21
2 should be [1 0;1 1], but for #3 notice that Mohammad wanted 4 zeros rather than 2.
Andrew Newell
2012-1-21
Right, but lowercase a is a 4 x 1 vector.
Walter Roberson
2012-1-21
Ah, I missed that different variables were being used.
更多回答（1 个）
Andrew Newell
2012-1-20
For 1. you could use
B = blkdiag(A,A);
For 2, why not just use the command you gave?
B=[A,zeros(2);A,A] ;
For 3:
B=[a' zeros(1,4); zeros(1,4) a']'
EDIT: Here is a generalization of 1:
n = 3; % e.g.
Amat = repmat(A,n,1);
Acell = mat2cell(Amat,2*ones(1,n),2);
B = blkdiag(Acell{:})
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2012-1-20
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