For loop for applying filter for each column

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Bharath
Bharath 2015-2-17
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
Greig 2015-2-17
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
Bharath 2015-2-19
编辑：Bharath 2015-2-19
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
Greig 2015-2-19
Your loop read through all of the columns, but since Xnew was overwritten each time, it only remembered the last loop.

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