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function y = fftw(x,sign)
%FFTW Discrete Fourier transform (DFT)
% Y = FFTW(X,SIGN) sets Y to the DFT of X, computed via a
% fast Fourier transform algorithm. SIGN is the sign of the
% exponent in the definition of the DFT, and should be +1 or -1.
%
% FFTW is designed for circumstances where repeated transforms
% of the same size are required. The first call will incur a
% substantial startup cost (several seconds), but subsequent
% calls will execute very quickly.
%
% Using SIGN = -1 corresponds to MATLAB's FFTN function.
% Using SIGN = +1 corresponds to an unnormalized IFFTN:
%
% FFTW(X,+1) is the same as IFFTN(X) * PROD(SIZE(X))
%
% Thus, FFTW(FFTW(X,-1),+1) / PROD(SIZE(X)) equals X.
%
% The input array X may have any dimensionality. If X
% is multi-dimensional, then a true multi-dimensional DFT
% will be computed.
%
% This is an interface to the FFTW C library, which is
% described at: http://www.fftw.org
%
% See also: FFT, IFFT, FFT2, IFFT2, FFTN, IFFTN, FFTSHIFT
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