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 
.
