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Duplicate Each Element in a Matrix without using Repelem or Repmat

Benjamin Ong さんによって質問されました 2019 年 10 月 31 日
最新アクティビティ Benjamin Ong さんによって コメントされました 2019 年 11 月 2 日
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

Adam
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

Fangjun Jiang
回答者: Fangjun Jiang
2019 年 10 月 31 日
編集済み: Fangjun Jiang
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

  1 件のコメント

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

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Stephen Cobeldick
回答者: Stephen Cobeldick
2019 年 10 月 31 日
編集済み: Stephen Cobeldick
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

  3 件のコメント

Benjamin Ong 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
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 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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