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Shift rows by different amounts

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Ellie
Ellie on 31 Jul 2015
Commented: Ellie on 31 Jul 2015
I have a N^2 x N^2 matrix where N = 4, and I wish to shift rows 1, 5, 9, and 13 by 0. Rows 2, 6, 10, 14 by 4. Rows 3, 7, 11, 15 by 8. Finally rows 4, 8, 12, 16 by 12. Ideally it would be a general code, as I plan to apply it to more than just this example. I have tried many things but to no avail. Any help would be appreciated. Thanks

Accepted Answer

Cedric Wannaz
Cedric Wannaz on 31 Jul 2015
Edited: Cedric Wannaz on 31 Jul 2015
N = 4 ;
A = repmat( 1:N^2, N^2, 1 ) ; % Dummy example.
for k = 2 : N
A(k:N:N^2,:) = circshift( A(k:N:N^2,:), (k-1) * N, 2 ) ;
end
With that, the the original A is:
A =
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
and the final:
A =
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
13 14 15 16 1 2 3 4 5 6 7 8 9 10 11 12
9 10 11 12 13 14 15 16 1 2 3 4 5 6 7 8
5 6 7 8 9 10 11 12 13 14 15 16 1 2 3 4
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
13 14 15 16 1 2 3 4 5 6 7 8 9 10 11 12
9 10 11 12 13 14 15 16 1 2 3 4 5 6 7 8
5 6 7 8 9 10 11 12 13 14 15 16 1 2 3 4
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
13 14 15 16 1 2 3 4 5 6 7 8 9 10 11 12
9 10 11 12 13 14 15 16 1 2 3 4 5 6 7 8
5 6 7 8 9 10 11 12 13 14 15 16 1 2 3 4
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
13 14 15 16 1 2 3 4 5 6 7 8 9 10 11 12
9 10 11 12 13 14 15 16 1 2 3 4 5 6 7 8
5 6 7 8 9 10 11 12 13 14 15 16 1 2 3 4
I am not sure that the solutions that don't involve a FOR loop are more efficient ultimately, because the FOR loop has only N-1 iterations and no realloc or conversion to/from cell arrays. You'd have to profile every approach to be sure.
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