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coherence estimates the coherence and cross-spectrum of a pair of real-valued time series; as a byproduct of its calculation of coherence, it also estimates the autospectra of each of its input time series. The file argument specifies the name of a text file containing the samples of the series in two columns. The standard output contains five columns of numbers (optionally preceded by column headings), which are frequency (Hz), coherence, cross-spectral power (dB), autospectral power (dB) of the first time series, and autospectral power (dB) of the second time series.
This program is based on a Fortran program by C.R. Arnold, G.C. Carter, and J.F. Ferrie, as described in `A coherence and cross-spectral estimation program', by G.C. Carter and J.F. Ferrie, in Programs for Digital Signal Processing, edited by the Digital Signal Processing Committee of the IEEE ASSP Society (New York: IEEE Press, 1979). The functions fft842() and its auxiliary functions r2tx(), r4tx(), and r8tx(), are based on Fortran subroutines by G.D. Bergland and M.T. Dolan, as described by them in `Fast Fourier transform algorithms', also included in Programs for Digital Signal Processing.
Options are:
Note that the scale factors generally have little or no visible effect on the coherence or on the shape of the spectra. The choice of chunk size (using the -n option) will have a significant effect; some experimentation may be needed to determine an appropriate chunk size in each case.
fft(1)
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PhysioNetUpdated 29 December 2004