For loop for applying filter for each column

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Bharath 2015-2-17

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评论： Greig 2015-2-19

Hi I've a signal which I read into matlab as a 4096x28 matrix. I want to apply for loop as follows which will read one column apply the filter and then store the values and then moves to the next column.

X = reshape(T_hor,[],28); % forming 4096x28 matrix 
 for i = 1:28;
  Xnew = X(:,i) - mean(X(:,i)); % filter for DC offset
 end;

It just reads the last column (28th) and stops. Is something wrong with my code? Can someone help me to fix this. Thanks in advance.

thanks in advance

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Greig 2015-2-17

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Xnew is not indexed. You should have Xnew(:, i).

You could do this without the loop. One such way would be...

Xnew = X - repmat(mean(X), 4096, 1);

Another is....

Xnew = detrend(X,0);

I would go with the second (less typing), but either will save you some time in a loop.

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Bharath 2015-2-19

编辑：Bharath 2015-2-19

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Thanks a ton. It was very informative and it works perfectly..! :) So is it always good to preallocate before start of a loop? In my previous case I just defined as

ii= 1:28

It just read only the last column but now it seems working perfectly good with the preallocation.

Greig 2015-2-19