How to create a 2D reverse matrix

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Anthony Koning
Anthony Koning 2022-10-17
编辑： John D'Errico 2022-10-17
Hi, I'm wondering how to create a reversed numerical matrix. For example, if I have a convolution h[j,k] = [1 2 3; 4 5 6; 7 8 9] then reverse h[j,k] = h[-j-k] = [9, 8 7; 6 5 4; 3 2 1]. I'm aware that you can use rot90(h, 2) and a combination of fliplr and flipud to get the results of reverse h, but are there any more direct ways to get the reverse matrix? Thanks.

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John D'Errico
John D'Errico 2022-10-17
编辑：John D'Errico 2022-10-17
Ran in:
Since you are willing to use tools like fliplr (as opposed to flip. Anyway, fliplr and flipud are more descriptive, so I kind of like them.) But then what is wrong with the simple:
H = [1 2 3; 4 5 6; 7 8 9]
H = 3×3
1 2 3 4 5 6 7 8 9
Hflip = fliplr(flipud(H))
Hflip = 3×3
9 8 7 6 5 4 3 2 1
which requires only 2 calls. Or, if you like a matrix multiply, you could do it as:
trans = flip(eye(3));
trans*H*trans
ans = 3×3
9 8 7 6 5 4 3 2 1

更多回答（1 个）

David Hill
David Hill 2022-10-17
Ran in:
a=[1 2 3; 4 5 6; 7 8 9];
reshape(flip(a(:)),size(a))
ans = 3×3
9 8 7 6 5 4 3 2 1

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