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how to add zeros around a matrix?

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Mucahid Akyar
Mucahid Akyar 2017-11-22
评论： DGM 2024-3-13
for example i have a matrix A = [1 2 3; 2 3 4; 5 6 7] I am working on image processing and I want to add zeros around this matrix like below. How can i do that?
0 0 0 0 0
0 1 2 3 0
0 2 3 4 0
0 5 6 7 0
0 0 0 0 0

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采纳的回答

Stephen23
Stephen23 2017-11-22
>> conv2(A,[0,0,0;0,1,0;0,0,0])
ans =
0 0 0 0 0
0 1 2 3 0
0 2 3 4 0
0 5 6 7 0
0 0 0 0 0
  5 个评论
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Stephen23
Stephen23 2017-11-22
编辑：Stephen23 2017-11-22
It is not clear what you would expect the result to be. MATLAB does not currently have a syntax for looping over two variables at once. You could define the loop to be an index and use that to select elements from those vectors:
iV = 0:1:5;
jV = 0:1:5;
for k = 1:numel(iV)
iN = iV(k);
jN = jV(k);
end
Eren Ozcelik
Eren Ozcelik 2021-4-30
Hi. How can I use this method for non-square matrix? For example creating a border for 1000x1500 matrix.

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更多回答（3 个）

KL
KL 2017-11-22
newA = zeros(size(A)+2);
newA(2:end-1,2:end-1)=A
Andrei Bobrov
Andrei Bobrov 2017-11-22
编辑：Andrei Bobrov 2017-11-22
padarray(A,[1 1],0)
  2 个评论
Stephen23
Stephen23 2017-11-22
Note: requires the image toolbox.
DGM
DGM 2022-7-16
While padarray() requires IPT, MIMT has padarrayFB(), which uses, but does not require IPT. That's a possibility for those who don't have IPT. ... but then MIMT also has other options for adding borders to images.

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noam gridish
noam gridish 2024-3-12
% create bigger mat of zeros
[m,n]=size(A);
paded_mat=zeros(m+1,n+1);
paded_mat(2:end-1,2:end-1)=A;
A=paded_mat;
  1 个评论
DGM
DGM 2024-3-13
Have you tested this? I ask because it will throw an error. Your preallocated array is too small.

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