function y=dft(x,N) 
%x為輸入信號(hào) 
%N為所取的點(diǎn)數(shù) 
y=zeros(1,N); 
for k=1:N 
for m=1:N 
y(k)=y(k)+x(m)*exp(-j*2*pi*(k-1)*(m-1)/N); 
end; 
end;function y=dft(x,N)
%x為輸入信號(hào)
%N為所取的點(diǎn)數(shù)
y=zeros(1,N);
for k=1:N
    for m=1:N
        y(k)=y(k)+x(m)*exp(-j*2*pi*(k-1)*(m-1)/N);
    end;
end; 


N=256;
x1=[1 1 1 1];
x=[x1 zeros(1,N-length(x1))];


L=1;
M=log2(N);
while L<=M
LE=2^L;
LE1=LE/2;
U=1;
W=exp(-j*2*pi/LE);
J=0;
while J<=LE1-1;
I=J;
while I<=N-1
IP=I+LE1;
T=x(I+1)+x(IP+1);
x(IP+1)=(x(I+1)-x(IP+1))*U;
x(I+1)=T;
I=I+LE;
end
U=U*W;
J=J+1;
end
L=L+1;
end
x;

NV2=N/2;
NM1=N-1;
I=0;
J=0;
while I<NM1
if I<J
T=x(J+1);
x(J+1)=x(I+1);
x(I+1)=T;
end
K=NV2;

while K<=J
J=J-K;
K=K/2;
end
J=J+K;
I=I+1;
end
x;

n=0:N-1;
q=n*2*pi/N;
stem(q,angle(x),'.')

---------------------------------------------
這是DIT-FFT的程序，我就是根據(jù)這個(gè)來修改的，測試通過，而DIF-FFT則波形不對(duì)。
N=256;
x1=[1 1 1 1];
x=[x1 zeros(1,N-length(x1))];

NV2=N/2;
NM1=N-1;
I=0;
J=0;
while I<NM1
if I<J
T=x(J+1);
x(J+1)=x(I+1);
x(I+1)=T;
end
K=NV2;

while K<=J
J=J-K;
K=K/2;
end
J=J+K;
I=I+1;
end
x;

L=1;
M=log2(N);
while L<=M
LE=2^L;
LE1=LE/2;
U=1;
W=exp(-j*2*pi/LE);
J=0;
while J<=LE1-1;
I=J;
while I<=N-1
IP=I+LE1;
T=x(IP+1)*U;
x(IP+1)=x(I+1)-T;
x(I+1)=x(I+1)+T;
I=I+LE;
end
U=U*W;
J=J+1;
end
L=L+1;
end
x;
n=0:N-1;
q=n*2*pi/N;
stem(q,abs(x),'.')