The FFT 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 FFT execution is a list of two Geo Time Series™ and a frequency scale factor per input GTS. The first resulting GTS contains the real parts of the FFT coefficients, the second the imaginary parts. 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.

FFT can only be applied to bucketized numerical Geo Time Series™ which contains a number of values which is a power of 2.

FFT is available since version 1.0.0.

See also



NEWGTS 1 512 <% 'k' STORE $k 1000 * 500 + NaN NaN NaN $k 180.0 / DUP SIN SWAP 100 * COS + ADDVALUE %> FOR DUP [ SWAP bucketizer.last 0 1000 0 ] BUCKETIZE FFT