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search  In mathematics, in the area of statistical analysis, the
trispectrum is a statistic used to search for nonlinear
interactions. The Fourier transform of the second-order
cumulant, i.e., the autocorrelation function, is the traditional
power spectrum. The Fourier transform of C4 (t1, t2, t3)
(fourth-order cumulant-generating function) is called the
trispectrum or trispectral density.  The trispectrum T(f1,f2,f3)
falls into the category of higher-order spectra, or polyspectra,
and provides supplementary information to the power spectrum.
The trispectrum is a three-dimensional construct. The symmetries
of the trispectrum allow a much reduced support set to be
defined, contained within the following verticies, where 1 is
the Nyquist frequency. (0,0,0) (1/2,1/2,-1/2) (1/3,1/3,0)
(1/2,0,0) (1/4,1/4,1/4). The plane containing the points
(1/6,1/6,1/6) (1/4,1/4,0) (1/2,0,0) divides this volume into an
inner and an outer region. A stationary signal will