The tapered periodogram it is given by
$$I(\lambda) = \frac{|D_n(\lambda)|^2}{2\pi
H_{2,n}(0)}$$ with \(D(\lambda) = \sum_{s=0}^{n-1} h
\left(\frac{s}{N}\right) y_{s+1}\,
e^{-i\,\lambda\,s}\), \(H_{k,n} = \sum_{s=0}^{n-1}h
\left(\frac{s}{N}\right)^k\,
e^{-i\,\lambda\,s}\) and \(\lambda\) are Fourier frequencies defined as
\(2\pi k/n\), with \(k = 1,\,\ldots,\, n\).
The data taper used is the cosine bell function,
\(h(x) = \frac{1}{2}[1-\cos(2\pi x)]\). If the series has missing data,
these are replaced by the average of the data and \(n\) it is corrected by
$n-N$, where \(N\) is the amount of missing values of serie. The plot of
the periodogram is periodogram values vs. \(\lambda\).