autocorrelation.jl

# return the autocorrelation of x
function ac(x)
    N = length(x)
    # zero pad x 
    x = [x,zeros(N-1)]
    R = irfft(abs(rfft([2,3,1,0,0])).^2, 2*N-1)
    R[1:N]
end

x = [2,3,1] 
print(ac(x))