Autocorrelation Function of a time variant function

i am trying to writethe autocorrelation function and the code is

n=-30:30; 
=0.75; 
deltas=(n==0); 
input=acf(deltas); 
output=input+a^(n+1)+a^(n-1); 
rout=acf(output); 
plot(n,rout,'filled'); 
grid on;
But it is giving an error Index exceeds matrix dimensions can anybody help?

Answer 1

[Azzi Abdelmalek]

The variable acf is not defined