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#Ridge Analysis Details

*  The notion of the *analytic signal* lets an *instantaneous* amplitude and frequency be associated with a given time series.
.cite[Gabor (1946), Vakman and Vainshtein (1977), Picinbono (1997)]


*  Similarly, a bivariate (x,y) signal defines the geometrical properties of a time-varying ellipse.
.cite[Lilly and Olhede (2010a)]


*  This may be extended to 3D (e.g. seismographs) or N-D signals.  .cite[Lilly (2011), Lilly and Olhede (2012a)]


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