FFTAP function computes a Fast Fourier Transform on a Geo Time Series™ or a list
thereof it expects on top of the stack.
The result of the
FFTAP execution is a list of two Geo Time Series™ and a frequency scale factor per input GTS. The first resulting GTS contains
the amplitude of the coefficient at that frequency and the second the associated phase. The scale factor is equal to X/(n * bucketspan) where n is
the number of elements in the origin GTS and X is the number of time units per second. The ticks of those Geo Time Series™ are indices from 0 to the
number of values in the original series minus one. The frequency associated with each tick is tick * factor, with the exception of tick 0 which is n * factor.
FFTAP can only be applied to bucketized numerical Geo Time Series™ which contains a number of values which is a power of 2.