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Fast Fourier Transform
Syntax y = fft(x)
Include: include spt\fft.oms
See Also fft , ifft

ARGUMENTS:
   INPUTS:
      x = MATRIX/VECTOR, any numerical type
   RETURN: MATRIX, COMPLEX

Description

Fast Fourier Transform. This is the typical FFT, listing the result in the standard order of non-negative frequency values first, followed by reversed negative frequency values. The function is identical to the O-Matrix "dft()" function. It has been provided here under the name "fft()" in order to make O-Matrix code more portable to other application and vice versa. When this function is loaded into the workspace with the command:

include spt\fft.oms

 it replaces the native version of the O-Matrix "fft()" function which is a "centered" version of the FFT. Clearing the workspace deletes this inclusion and so it must be included again to allow subsequent use. The matching "ifft(x)" SPT function also produces matching standard FFT behavior.

Example
Do the FFT of a single cycle of a cosine waveform:

include spt\fft.oms
N    = 8;              # FFT sample length
t    = seq(N)-1d0;     # time vector
x    = cos(2*PI*t/N);  # Signal to transform
YFFT = fft(x);         # Do FFT
format complex "f5.2";
YFFT

 O-Matrix responds with:

{
(-0.00, 0.00)
( 4.00,-0.00)
( 0.00, 0.00)
(-0.00,-0.00)
( 0.00, 0.00)
(-0.00, 0.00)
( 0.00, 0.00)
( 4.00, 0.00)
}