set verbose off
nulldata 50
set seed 76543
# generate an AR(1) process
series e = normal()
series x = 0
x = 0.9*x(-1) + e

# compute the periodogram

F = fft({x}) # note that the series is turned into a matrix on the fly 
S = abs(F).^2
S = S[2:($nobs/2)+1] / (2*$pi*$nobs)
sfreq = seq(1,($nobs/2))'
omega = sfreq .* (2*$pi/$nobs)
period = $nobs ./ sfreq
omega = omega ~ sfreq ~ period ~ S

# compare the built-in command
pergm x
print omega