第四章快速傅里叶变换 补充内容 与本章内容有关的 MATLAB知识 Discrete fourier transform tax Y=fit(X) Y=fft(x, n) Y=fft(x, 0, dim Y=fft(X, n, dim) Definition The functions X=fit(x)and x= ifft(X) implement the transform and inverse transform pair given for vectors of length by (k)=∑x()o x()=∑x(k)ok where -(2zi) is an Nth root of unity Description Y= fit(X) returns the discrete Fourier transform(DFT)of vector X, computed with a fast Fourier transform(FFT)algorithm IfX is a matrix. fft returns the fourier transform of each column of the matrix If X is a multidimensional array, fft operates on the first nonsingleton dimension第四章 快速傅里叶变换 补充内容： 与本章内容有关的 MATLAB 知识 1、fft ——Discrete Fourier transform Syntax Y = fft(X) Y = fft(X,n) Y = fft(X,[],dim) Y = fft(X,n,dim) Definition The functions X = fft(x) and x = ifft(X) implement the transform and inverse transform pair given for vectors of length by: ( ) ( ) ( 1 1 )( ) 1 j k N N j X k x j  − − = = ( ) ( ) ( 1 1 )( ) 1 1 N j k N k x j X k N  − − − = =  where (2 i) N N e   − = is an Nth root of unity. Description Y = fft(X) returns the discrete Fourier transform (DFT) of vector X, computed with a fast Fourier transform (FFT) algorithm. If X is a matrix, fft returns the Fourier transform of each column of the matrix. If X is a multidimensional array, fft operates on the first nonsingleton dimension