Circshift an ND array by values in an (N-1)D array w/out for loop

2017 6 19
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更新时间：2017 6 21
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I have an ND array A that I would like to circshift (in its Nth dimension) by the corresponding values in an (N-1)D array b, ideally without a for loop (and/or fft/ifft). For example:
A(:,:,1) =
1 3 5
2 4 6
A(:,:,2) =
7 9 11
8 10 12
A(:,:,3) =
13 15 17
14 16 18
A(:,:,4) =
19 21 23
20 22 24
b =
1 -1 -3
-1 -1 0
with the result:
A_shift_b(:,:,1) =
19 9 23
8 10 6
A_shift_b(:,:,2) =
1 15 5
14 16 12
A_shift_b(:,:,3) =
7 21 11
20 22 18
A_shift_b(:,:,4) =
13 3 17
2 4 24
I've been trying to use arrayfun to get to a solution, but so far have been unsuccessful. Any help would be appreciated. Thanks!

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Andrei Bobrov
Andrei Bobrov 2017-6-19
编辑：Andrei Bobrov 2017-6-19

1 个投票

A = reshape(1:24,[2 3 4]);
b = [1 -1 -3
-1 -1 0];
[m,n,k]= size(A);
A1 = reshape(A,[],k);
mn = m*n;
try
out = reshape(A1((1:mn)'+mn*rem((1:k) - b(:) + k-1,k)),[m,n,k]);% R2016b and later
catch
out = reshape(A1(bsxfun(@plus,(1:mn)',...
mn*rem(bsxfun(@minus,1:k,b(:)) + k-1,k))),[m,n,k]); %R2016a and earlier
end

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Ty Easley
Ty Easley 2017-6-21
编辑：Ty Easley 2017-6-21
Could you explain the the role played by (1:k) in this code? It seems to me that it would require length(1:k) = length(b(:)), except that condition doesn't hold in the example given and the code still works. In addition, why doesn't (1:k) - b(:) throw an error, since one is a row vector and the other a column vector? I have started getting a "matrix dimensions must agree" error from this code and am not sure why I didn't earlier on.
Ty Easley
Ty Easley 2017-6-21
(and, fyi, the bsxfun catch does properly evaluate, but I'm also running on R2016b, so I'm curious about why the "try" code hits an error)

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