if you are trying to insert xsim1 between x(i) and x(i+1) without any data loss, write this code:
x = [x(1:i), xsim, x(i+1:end)]
the value is injected to your vector meaning that if its previous length was "n" now it is "n+1". notice that if you use this in a for loop, the size of your vector changes periodically. in order to avoid that, you have to preallocate the final vector size. if you do this, then it means rather than inserting value you must assign value which is more efficient.
