C94alt.m

 Y=[0 0];
k=0:11; 
f=[0 0 4.^(k)];
for m=1:length(k)
y=-6*Y(m+1)-9*Y(m)+2*f(m+2)+6*f(m+1);
Y=[Y y];
end
k=[0 0 k];
stem(k,Y)