the fft file by myself

fft

function Y=zjfft(x) %????FFT??????????
tic;
x1=changeorder(x); %?????????
N=length(x1); %???????
M=log2(N); %???????
Y=zeros(1,N); %???????N???
B=zeros(1,N);
%------------??????????---------------
Y=x1;
%-------------------??-----------------------

for i=1:M
B=Y;
for r=1:N
%B=Y;
zf=((-1).^floor((r-1)/(2.^(i-1)))); %???
W=exp(-j*2*pi*mod(r-1,2.^(i-1))/2.^i); %?????
Y(r)=zf*B(r)*W.^((zf-1)/(-2))+W.^((zf+1)/2)*B(r+zf*2.^(i-1)); %??????
end
end
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