$(1\mathrm{.}25$ points$)$ Determine the output $y(n),1n15$ for the following difference equation using a MATLAB function which accepts $n$ as the input.

$y(n)+\frac{3}{4}y(n-1)+\frac{1}{8}y(n-2)=u(n-1)$;$y(0)=1,y(-1)=-6$

where the input $u(n)=(\frac{1}{2}{)}^n,n0.($Be careful about the indices, because MATLAB starts a vector with the index of $1.)$