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**lomb** transforms a real-valued time series
(from the specified *input-file*, or from the standard input if *input-file*
is specified as "-"; *input-file* must be in text form) into a power spectrum
(on the standard output), using a technique known as the Lomb periodogram.

The input is a text file containing a sampled time series, presented as
two columns of numbers (the sample times and the sample values). The intervals
between consecutive samples need not be uniform (in fact, this is the most
significant advantage of the Lomb periodogram over other methods of power
spectral density estimation). **lomb** writes the Lomb periodogram (the power
spectral density estimate derived from the input time series) on the standard
output, in two columns (frequency and power). If the units of the sample
times in the input file are seconds, the units of the frequencies in the
output are Hz.

*Options* are:

**-h**- Print a usage summary.
**-P**- Generate a power spectrum (print squared magnitudes).
**-s**- Smooth the output.
**-z**- Add a constant to each input sample, chosen such that the mean value of the entire series is zero.

Among many other applications, this program can be used to estimate heart
rate power spectra, in combination with **ihr**(1)
. The Lomb method is ideal
for analysis of any time series with missing or noisy data (the noisy data
may be removed from the time series and need not be replaced, as would
be necessary if conventional PSD estimation algorithms were employed).

- Lomb, N.R.
- Least-squares frequency analysis
of unequally spaced data.
*Astrophysics and Space Science***39**:447-462 (1976). - Press, W.H, and Rybicki, G.B.
- Fast algorithm for spectral analysis of unevenly
sampled data.
*Astrophysical J.***338**:277-280 (1989). - Press, W.H. Teukolsky, S.A., Vetterling, W.T., and Flannery, B.P.
*Numerical Recipes in C: the Art of Scientific Computing*, pp. 575-584 (Cambridge Univ. Press, 1992).- Moody, G.B.
- Spectral analysis
of heart rate without resampling.
*Computers in Cardiology 1993*, pp. 715-718 (IEEE Computer Society Press, 1993). http://www.physionet.org/physiotools/lomb/lomb.html .

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