"for" loop question

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

Answer 1

[Matt J]

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

Answer 2

[Cedric]

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.

Answer 3

[NH]

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