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The first three of these UNIX shell scripts are intended to illustrate the use of fft(1) , lomb(1) , and memse(1) by producing heart rate power spectra using the fast Fourier transform, the Lomb periodogram, and the maximum entropy (all poles) method (also known as autoregressive, or AR, power spectral density estimation). All four programs derive heart rate time series from beat annotation files. hrfft and hrmem use tach(1) to obtain a uniformly resampled heart rate time series from the annotation file, which is then used as input to fft or memse, and the spectrum thereby obtained is then plotted. hrlomb and hrplot use ihr(1) to obtain an irregularly sampled heart rate time series. hrplot plots this time series directly, and hrlomb uses it as input to lomb, and then plots the spectrum.
All four programs accept the same options:
If annotator or record are not specified using environment variables or command-line options, these programs obtain values from the user interactively.
Although hrfft, hrlomb, and hrmem all produce power spectra, the units of power differ among them. Absolute comparisons can be made only between spectra produced using the same method, from time series of the same length.
Note that these shell scripts can be run under MS-DOS using a suitable set of UNIX-like utilities, such as the MKS Toolkit or the GNUish MS-DOS utilities, and under MS-Windows using the free Cygwin package.
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Updated 8 March 2019