使用matlab实现FFT_FFT.zip

function x=fft_def(x) %tic N=length(x); %xput=zeros(1:Nnew); if(rem(log2(N),1)~=0) Nnew=2^(floor(log2(N))+1); new=zeros(1,Nnew-N); x=[x new]; N=Nnew; end Nl=N;%个数 %xput=zeros(1:N); Nn=1;%序列个数 % buffer=0;%交换值时需要一个缓存变量 Nh=N/2;%每个序列点个数 w=-1i*2*pi; W=zeros(1,N/2-1); W(1)=exp(w/Nl); for i=2:N/2-1 W(i)=W(1)*W(i-1); end %index=0;%索引 %toc while(N>1) % tic for i=0:Nn-1 for j=1:Nh up=i*N+j; down=up+Nh; buffer=x(up); x(up)=x(up)+x(down); % disp("up"); % disp(up); % x(down)=x(up)-x(down)-x(down); x(down)=buffer-x(down); % disp("down"); % disp(down); % x(down)=x(down)*exp(w*(j-1)/N); % disp(j-1); % disp(x(down)); if((j-1)~=0) index=(j-1)*Nn; % disp(index-1); % if(W(index)==0) % W(index)=exp(w*index/Nl); % end x(down)=x(down)*W(index); end % if(index~=1) % x(down)=x(down)*W(index); % end end end % toc N=N/2; % disp("N"); % disp(N); Nh=N/2; Nn=Nn*2; end %disp(Nl); % flag=ones(1,Nl); % for i=1:Nl % first=i; % % next=bitreverse(log2(Nl),i-1)+1; % next=1; % if(first~=next&&flag(first)&&flag(next)) % buffer=x(first); % x(first)=x(next); % x(next)=buffer; % flag(first)=0; % flag(next)=0; % end % end j1 = 0; for i = 1 : Nl if i < j1 + 1 tmp = x(j1 + 1); x(j1 + 1) = x(i); x(i) =tmp; end k = Nl / 2; while k <= j1 j1 = j1 - k; k = k / 2; end j1 = j1 + k; end end