*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
[Lomb, N.R., ``Least-squares frequency analysis of unequally spaced data'', *Astrophysics
and Space Science* 39:447-462 (1976)].

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.
**-s**- Smooth the output.

The original version
of this program was based on the algorithm described in Press, W.H, and
Rybicki, G.B., ``Fast algorithm for spectral analysis of unevenly sampled
data'', *Astrophysical J.* 338:277-280 (1989). It has been rewritten using the
version of this algorithm presented in 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).

Among many other applications,
this program can be used to estimate heart rate power spectra, in combination
with *ihr* (see Moody, G.B., ``Spectral analysis of heart rate without resampling'',
*Computers in Cardiology 1993*, pp. 715-718 (IEEE Computer Society Press,
1993)). 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).

This
program is part of the *psd* package, distributed with the DB Software Package,
version 9.3 and later.