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+@code{(require 'fft)}
+@ftindex fft
+
+
+@defun fft array
+
+@var{array} is an array of @code{(expt 2 n)} numbers.  @code{fft}
+returns an array of complex numbers comprising the
+@dfn{Discrete Fourier Transform} of @var{array}.
+@cindex Discrete Fourier Transform
+@end defun
+
+@defun fft-1 array
+
+@code{fft-1} returns an array of complex numbers comprising the
+inverse Discrete Fourier Transform of @var{array}.
+@end defun
+@noindent
+@code{(fft-1 (fft @var{array}))} will return an array of values close to
+@var{array}.
+
+@example
+(fft '#(1 0+i -1 0-i 1 0+i -1 0-i)) @result{}
+
+#(0.0 0.0 0.0+628.0783185208527e-18i 0.0
+  0.0 0.0 8.0-628.0783185208527e-18i 0.0)
+
+(fft-1 '#(0 0 0 0 0 0 8 0)) @result{}
+
+#(1.0 -61.23031769111886e-18+1.0i -1.0 61.23031769111886e-18-1.0i
+  1.0 -61.23031769111886e-18+1.0i -1.0 61.23031769111886e-18-1.0i)
+@end example