**almost perfect sequences**

### Definitions

Let n be a positive integer. A binary almost perfect sequences
of length n is a mapping f from the cyclic group Z/nZ into
{-1,+1} whose the autocorrelation values are 0 except two
times.

fxf(0) = n, fxf(n/2)=4-n
The length of a such sequence is a multiple of 4 but
one conjectures that such sequence exists if and only
if n = 2 (q+1) where q is a power of a prime.
### code

One can use the finite field GF(q^2) to construct
a sequence of length 2(q+1). An implantation of
the methode of Bradley and Pott is given by the
three files below. Enjoy !

Philippe Langevin,
Last modification, june 2017.