## Duplicate Each Element in a Matrix without using Repelem or Repmat

Benjamin Ong

### Benjamin Ong (view profile)

さんによって質問されました 2019 年 10 月 31 日

### Benjamin Ong (view profile)

さんによって コメントされました 2019 年 11 月 2 日
Fangjun Jiang

### Fangjun Jiang (view profile)

さんの 回答が採用されました
Is there a way I can make each element in a matrix duplicate into a 3 by 3? if
A=[1 0;0 1]
Is there a way i can turn it into
Aew=[1 1 1 0 0 0;1 1 1 0 0 0;1 1 1 0 0 0;0 0 0 1 1 1;0 0 0 1 1 1;0 0 0 1 1 1]
so basically
Anew=repelem(A,3,3)
but without repelem, repmat or any special functions?
Thanks

#### 1 件のコメント

2019 年 10 月 31 日
Yes, but the only reason I can see for wanting to do so is as a homework question. Like most things you can do it with a for loop.

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## 2 件の回答

2019 年 10 月 31 日

### Fangjun Jiang (view profile)

2019 年 10 月 31 日
採用された回答

a=eye(2);
k=3;
d=blkdiag(ones(k,1),ones(k,1));
b=d*a*d'
%%Or a more generic case
a=[1 2 3;4 5 6];
k=3;
[m,n]=size(a);
d1=ones(k,1)*ones(1,m);
d1=mat2cell(d1,k,ones(1,m));
d1=blkdiag(d1{:});
d2=ones(n,1)*ones(1,k);
d2=mat2cell(d2,ones(n,1),k);
d2=blkdiag(d2{:});
b=d1*a*d2

Benjamin Ong

### Benjamin Ong (view profile)

2019 年 11 月 1 日
Thanks this helped alot :D

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2019 年 10 月 31 日

### Stephen Cobeldick (view profile)

2019 年 10 月 31 日

>> A = [1,0;0,1]
A =
1 0
0 1
>> V = ceil((1:6)/3);
>> B = A(V,V)
B =
1 1 1 0 0 0
1 1 1 0 0 0
1 1 1 0 0 0
0 0 0 1 1 1
0 0 0 1 1 1
0 0 0 1 1 1

Benjamin Ong

### Benjamin Ong (view profile)

2019 年 11 月 1 日
This way only seems to produce a 2 by 2 everytime though no matter the size of the initial matrix
Stephen Cobeldick

### Stephen Cobeldick (view profile)

2019 年 11 月 2 日
"This way only seems to produce a 2 by 2 everytime though no matter the size of the initial matrix"
Clearly it works, as the example in my answer shows.
Of course it can be trivially adjusted to replicate the elements of any sized array any number of times, to do so requires two very small changes to the V definition:
k = 3;
V = ceil((1:k*size(A,1))/k);
This is certainly a much simpler and more efficient solution than the one that you accepted.
Benjamin Ong

### Benjamin Ong (view profile)

2019 年 11 月 2 日
Ahh ya I did realise your method is simpler but i was having big brainfart at the moment and the solution i accepted I seem to understand how it works better? But thanks for the help anyways :D

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