fftmn.m

很多matlab的源代码

function y =fftmn(x,R,C)
%FFTMN	FFT of a data set from fft of its smaller subsets
%	y=fftmn(x,R,C) FFT of x using fft of R rows and C columns
%	Length(x)  must equal RC
%
%	If no input arguments are given, the following example is used
%	Find fft of z=[1:12] using 4 rows and 3 columns and compute error
%	z=(1:12)';Z=fft(z);Zmn=fftmn(z,4,3);err=Z-Zmn


% ADSP Toolbox: Version 2.0 
% For use with "Analog and Digital Signal Processing", 2nd Ed.
% Published by PWS Publishing Co.
%
% Ashok Ambardar, EE Dept. MTU, Houghton, MI 49931, USA
% http://www.ee.mtu/faculty/akambard.html
% e-mail: [e-mail]
% Copyright (c) 1998



if nargin==0,help fftmn,disp('Strike a key for results of the example'),pause
z=(1:12)';Z=fft(z);Zmn=fftmn(z,4,3);err=Z-Zmn,return,end

N=length(x);
if nargin<3, C=1;end
if nargin<2, R=N;end
if N~=R*C,error('length(data) must equal (rows)*(columns)'),return,end

%Reshape x into an RxC matrix (fill along columns)
y=reshape(x,R,C);


%Replace each row by its DFT times W_r=exp(-j*2*pi*r*c/N)
%where r=0 for first row, r=1 for second row etc and c=0:C-1; for each row

for k=1:R
y(k,:)=fft(y(k,:)).*exp(-j*2*pi*(k-1)*(0:C-1)/N);
end

%Now, replace each column by its DFT. 

for k=1:C
y(:,k)=fft(y(:,k));
end

%Read out the result by rows
y=y.';y=reshape(y,size(x));

%y=y(:); %Convert to columns
%[row,col]=size(x);
%if row==1,y=y.';end