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Tia
0

what can i do for this problem?

Asked by Tia
on 27 Jul 2013

i want to use circshift on each 4096 blocks. each block has 8x8. what can i do?

example :

val(:,:,1) =
    1.0e+003 *
      1.5601   -0.0420    0.0307   -0.0164   -0.0116   -0.0204   -0.0001   -0.0001
     -0.0117    0.0063   -0.0138   -0.0298   -0.0134   -0.0001    0.0009    0.0003
     -0.0000   -0.0066   -0.0154    0.0001   -0.0002   -0.0007    0.0000    0.0001
      0.0139    0.0092    0.0001   -0.0004    0.0006    0.0000    0.0001   -0.0002
      0.0001    0.0003    0.0004   -0.0003   -0.0001    0.0005   -0.0000    0.0003
     -0.0002    0.0001    0.0001   -0.0003   -0.0003    0.0003    0.0000    0.0001
     -0.0004   -0.0003   -0.0002   -0.0002   -0.0001   -0.0004   -0.0001    0.0001
      0.0001   -0.0004   -0.0000    0.0002   -0.0000   -0.0002    0.0002    0.0003

until

val(:,:,4096) =
    888.0000  -17.6230   -5.2495   -0.4683         0    0.0909   -0.2610   -0.2792
     18.2375   12.0902  -14.1269  -10.2305  -13.2117   -0.1457   -0.2282    0.0176
     -6.8663    6.7403    8.3676   11.7774   -0.3663    0.1670   -0.3018   -0.3649
     20.8197   -0.1267  -10.9207    0.2049   -0.1160   -0.0591    0.1562   -0.2024
      0.2500   -0.2738         0   -0.2663   -0.2500    0.8486         0    0.0949
     12.3305   -0.2777   -0.7394   -0.1323   -0.1247   -0.0385    0.4240   -0.1999
      0.4087    0.2580   -0.0518    0.5184    0.4223    0.2034   -0.1176    0.2729
      0.1247    0.4444    0.1992   -0.2810    0.2159    0.2496   -0.2789   -0.2565

thanks

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2 Answers

Answer by Azzi Abdelmalek
on 27 Jul 2013
 Accepted Answer

val=rand(8,8,4096); % Example 
m=size(val,3);
a=arrayfun(@(x) circshift(val(:,:,x),-1),1:m,'un',0);
out=reshape(cell2mat(a),8,8,[]);

  5 Comments

oh.. i got it. it works.thanks

@Azzi: Again I suggest to avoid anonymous functions, here in arrayfun. See some timings in my answer.

@Azzi: No idea why the first comment was there. I have some timing problems in the forum currently. Sometimes after I hit the Save butting, its title is saved to "Saving..." and nothing happens for a minute. Then it is set back to "Save" without any changes.

I've deleted the misplaced first comment.

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Answer by Jan Simon
on 27 Jul 2013
Edited by Jan Simon
on 27 Jul 2013

There is no need to encapsulate circshift in arrayfun:

val = rand(8,8,4096);
tic;
m = size(val,3);
a = arrayfun(@(x) circshift(val(:,:,x),-1),1:m,'un',0);
out = reshape(cell2mat(a),8,8,[]);
toc
% Elapsed time is 0.411869 seconds.

A simple loop is faster than ARRAYFUN:

tic;
out2 = zeros(size(val));
for k = 1:m
  out2(:,:,k) = circshift(val(:,:,k), -1);
end
toc
% Elapsed time is 0.379831 seconds.

But circshift operate on 3D arrays directly also:

tic;
out3 = circshift(val, -1);
toc
% Elapsed time is 0.006587 seconds.
isequal(out, out2, out3)
% TRUE

This is 62 times faster (R2009a/64/Win7) and looks much easier.

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