Help with for loop - How do I use indices to denote intervals?

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Kristen
Kristen 2013-10-12
评论： Kristen 2013-10-12
I have a vector A, for example (1:1:600)'.
I have a matrix B with indices denoting which rows of A that I want to perform a calculation on. These indices are in intervals - B(:,1) is the start and B(:,2) is the end of each interval - for example B(:,1)=[5,15,25,35,45] and B(:,2)=[10,20,30,40,50] (corresponding to intervals 5-10,15-20,25-30,35-40,45-50).
I want to use the intervals specified in B to change something about A. This needs to happen for various reasons in my data, but for simplicity let's say I want to change values in the rows corresponding to those intervals to zero. I have been trying to use a for loop but I am missing something.
I have: for i=B(:,1); for j=B(:,2); A(i:j,:)=0; end; end;
Now, I would hope that this would change the values of rows 5-10,15-10,25-30,35-40,45-50 to 0, but the command is only executed for the first interval (rows 5-10), not the rest.
I am pretty new to Matlab and so I am sure I am missing some subtle and easy thing here. I have tried searching through all of the help topics and other people's questions but I can't find anyone else trying to use the indices as intervals.

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Azzi Abdelmalek
Azzi Abdelmalek 2013-10-12
编辑：Azzi Abdelmalek 2013-10-12
Edit
n=size(B,1);
for k=1:n;
ii=B(k,1)
jj=B(k,2)
A(ii:jj,:)=0;
end
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sixwwwwww
sixwwwwww 2013-10-12
Dear Kristen, you can do like this:
A = [1:600]';
B = [1:24]';
count = 0;
for i = 1:2:length(B)
multicative = 50;
C(i, :) = A(5 + multicative * count:10:45 + multicative * count);
C(i + 1, :) = A(10 + multicative * count:10:50 + multicative * count);
count = count + 1;
end
disp(C)
Now you can take values form Matrix C for corresponding indices in vector A. I hope it is what you need if I understood correctly. Good luck!

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