MATLAB: Hii I am not understanding this code please help and explain me step by step and please explain me idx2 = [0, idx, 0] what does it do.

mathematicsMATLAB

idx = EV > 0;
if iscolumn(idx), idx = idx'; end;
idx2 = [0, idx, 0];
prePt = [];  postPt = [];
for i = 2 : length(idx2)-1
    if idx2(i-1) == 0 & idx2(i) == 1 & idx2(i+1) == 1
        prePt = [prePt, i-1];
    end
      if idx2(i-1) == 1 & idx2(i) == 1 & idx2(i+1) == 0
          postPt = [postPt,i-1];
      end
  end
segNum = length(prePt);
segment = [];
for k = 1 : segNum
    segment(k,:) = [prePt(k), postPt(k)];
end

Best Answer

That bit of code concatenates zeroes onto both ends of the vector idx, and allocates this lengthened vector to a new variable idx2. Like this:
>> X = [5,6,7];
>> [0,X,0]
ans =   0   5   6   7   0
This is because the [] is a concatenation operator (not a list generation operator like lots of beginners think). Read this for more info on []:
http://www.mathworks.com/help/matlab/ref/specialcharacters.html
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