MATLAB: Subscript indices must either be real positive integers or logicals.

indices

i got this error in this code i don't know why.
c=[x(1:end-1,:),x(2:end,:)];
      dx=c(:,2)-c(:,1);
      t=[y(1:end-1,:),y(2:end,:)];
      dy=t(:,2)-t(:,1);
      ra=[];
      rb=[];
     for i=1:size(dx)
         if   dx(2i-1)>0 & dy(2i)<0;
             ra(2i-1)=1;
             ra(2i)=1;
         end
           if dy(2i-1)>0 & dx(2i)<0;
             rb(2i-1)=1;
             rb(2i)=1;
           end
     end

Best Answer

It's hard to tell without having some input, but these types of lines are definitely wrong:
ra(2i)=1;
i is being interpreted as imaginary, which is why you should not use i as a looping variable.
ans =
   0.0000 + 2.0000i
Could be other errors as well.
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