The aperiodic autocorrelation of a finite sequence 
of complex numbers is the sequence
 |
for 
, where 
denotes the complex conjugate
(Tang et al. 2018; Seberry and Yamada 2020, p. 33). Indices do not wrap
around the ends of the original sequence; terms without
an overlapping partner are omitted. By contrast, periodic
autocorrelation wraps indices modulo 
.
The two autocorrelations agree at 
but generally differ for 
.
