wheres the problem of this fiter code

bb1=[1,-0.9];

imp=1;

M=22;

r=0.9;

l=0:M;

bb2=r.^l;

HH=filter(bb1,1,bb2);

ZZ = filter(HH,1,imp)

nn=0:(length(HH)-1);

stem(nn,ZZ(nn+1));

xlabel('(n)')

ylabel('impulse response')

Answer 1

[Henrik]

Without any explanations of your code it's hard to tell, but my guess would be that

ZZ = filter(HH,1,imp)

should be

ZZ = filter(imp,1,HH);

This gives no errors, but I don't know if it's correct.