can anybody explain the commented line of the code

Are you asking this commented line?

% Y=[Y(:);X(end)];

>> X = [-2 1 -3 5 -1 3 -4 4 -2]

X =

         -2.00          1.00         -3.00          5.00         -1.00          3.00         -4.00          4.00         -2.00

>> Y=[1 2 3 4 5 6 7 8 9]

Y =

          1.00          2.00          3.00          4.00          5.00          6.00          7.00          8.00          9.00

>> Y=[Y(:);X(end)]

Y =

          1.00
          2.00
          3.00
          4.00
          5.00
          6.00
          7.00
          8.00
          9.00
         -2.00