# "for" loop question

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NH on 7 Feb 2013
Hello,
Below is an excerpt from my code, in which I wish to linearly fix a baseline drift. The variable "QLBrainShift1" is simply the original signal.
AmtOfPts1 = iSO(3) - iSO(2); % Amount of points between SO 2 and 3
error1 = -QLBrainShift1(end); % scalar
for point1 = AmtOfPts1:-1:0
QLBrainShift1a = QLBrainShift1+error1-(point1/AmtOfPts1)*error1;
end
figure
plot(QTime(iSO(2):iSO(3)),QLBrainShift1a)
The plot that is being returned seems like QLBrainShift1a is being overwritten upon each loop. Therefore, only the last loop (point1=0) exits the "for" loop, and gets plotted. My intention is to create a new signal (QLBrainShift1a) according to the equation above with varying "point1" values, and plot all of the new signal on 1 graph. Any help is greatly appreciated.
Thanks, NH

Matt J on 7 Feb 2013
Edited: Matt J on 7 Feb 2013
Perhaps as follows? Basically, you've forgotten to index the element of QLBrainShift1a (and maybe also QLBrainShift1) that you're trying to operate on.
point1=AmtOfPts1:-1:0;
for i=1:length(point1)
QLBrainShift1a(i) = QLBrainShift1(i)+error1-(point1(i)/AmtOfPts1)*error1;
end

Cedric Wannaz on 7 Feb 2013
Edited: Cedric Wannaz on 7 Feb 2013
I can't figure out what you are trying to do, but here are some bits of code that may simplify the discussion..
Assume that we have the following
>> data = [4, 5 ,8, 7, 10, 9, 10, 11] ;
>> plot(data, '*') ; % Just to visualize.
which follows a line except for two points. If you wanted to subtract e.g. the 1st value from all elements of data, you would do
>> data = data - data(1)
data =
0 1 4 3 6 5 6 7
>> plot(data, '*') ; % Just to visualize.
If you wanted to e.g. subtract values according to the slope between data(1) and data(end), you could do
>> n = numel(data) ;
>> slope = (data(end)-data(1))/(n-1) ;
>> data = data - (0:n-1)*slope
data =
0 0 2 0 2 0 0 0
>> plot(data, '*') ; % Just to visualize.
All that could be contracted into
>> data = [4, 5 ,8, 7, 10, 9, 10, 11] ;
>> n = numel(data) ;
>> data = data - data(1) - (0:n-1)*(data(end)-data(1))/(n-1) ;
Is there something in there that could be adapted to your case? If not, you should maybe provide a short example of the data that you have and what you would like to obtain.

NH on 7 Feb 2013
Matt J,
Yes! Thank you, I knew it was something simple I was missing. Your time is greatly appreciated.
Cedric, thanks for your time as well. Helped me understand it a bit more.
-NH