MATLAB: Matlab accuracy in linear functions

matlab accuracy zickzack

Hello fellows,
help me understand Matlab accuracy. I try modeling simple “zick-zack” signal:
      x=0:dt:4;
      slope=0.1;    
      h=(numel(x)-1)/4;
      y(1:h+1)=x(1:h+1)*slope;
      y(h+2:3*h+1)=2*y(h+1)-(x(h+2:3*h+1)*slope);
      y(3*h+2:4*h+1)=4*y(3*h+1)+(x(3*h+2:4*h+1)*slope);
and the last entry of y results to be -1,11022302462516e-16. I understand that there is a limit of accuracy but why here? Can you explain it for me or point my mistake
P.S:
In the end I change script to:
      y(1:h+1)=x(1:h+1)*slope;
      y(h+2:3*h+1)=2*y(h+1)-(x(h+2:3*h+1)*slope);
      y(3*h+2:4*h+1)=y(2:h+1)-0.1;
and now I can search for all x=0 entries
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