How can I read the elements of an array backwards?

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Konstantinos 2016-5-18

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https://ww2.mathworks.cn/matlabcentral/answers/284848-how-can-i-read-the-elements-of-an-array-backwards

回答： Johannes Kalliauer 2021-4-19

采纳的回答： Ahmet Cecen

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I have an array with x = 250000 elements. I want the code to read backwards a part of it:

k = pks3(1):-1:1; 
%read data points backwards starting from pks3 and ending at the beginning

So even though I have i = 10 pks3 peak points, I want to create an array k from the first point pks3(1). But, the problem is that in the end I get k = 255997855 elements, in which the pks3 point for example is repeated for several hundreds of times. The rest of the code is this:

      k = pks3(1):-1:1;
%read data points backwards starting from pks3 ending to pks3 again.
      first = k(k<xfb1); % find all k such that k is smaller than xfb1
      if ~isempty(first)
          first = first(1); %store the first number which is smaller than xfb1
      else
          disp('No value of k is smaller than xfb1.')
      end
      distQ = length(first:pks3(1));
      Qstart = locs_RwaveB(1)*distQ;  %distance from locs_RwaveB to Qstart point