function?[Xfreq]=shcenteredFFT（xFs）
%?this?is?a?custom?function?that?helps?in?plotting?the?autocorrelation?two-sided
%?spectrum
%?x?is?the?signal?that?is?to?be?transformed
%?Fs?is?the?sampling?rate
N=length（x）;
%?frequency?axis
if?mod（N2）==0
k=-N/2:N/2-1;?%?N?even
else