已经有100万个点，要求FFT，
A1=load('D:\。。。\sc1004.dat');
A1=A1-mean(A1);
A2=load('D:\。。。\sc2004.dat');
A2=A2-mean(A2);
A3=load('D:\。。。\SC1005.dat');
A3=A3-mean(A3);
A4=load('D:\。。。\SC2005.dat');
A4=A4-mean(A4);
B1=abs(fft(A1(99900:200000),1000000));
这里计算A1的幅值，但是没有明白fft((99900：2000000),1000000)啥意思，下面的又不要，而且说是取8192个点 ———
B2=abs(fft(A2,1000000));
B3=abs(fft(A3,1000000));
B4=abs(fft(A4,1000000));
%t=0:0.01:10000.03;
%z=(t');
%plot(z,A1)
%B1=B1(1:500000);
%B2=B2(1:500000);
%B3=B3(1:125000);
%B4=B4(1:125000);
U1=B2./B1;
U2=B4./B3;
F=0
100000000)/999999
100000000);
f=(F');
U1=U1/max(U1);
U2=U2/max(U2);
%Plot(f,U1,'r',f,U2,'k')
%semilogx(f,U1,'r',f,U2,'k')
%loglog(F,UF1,'r',F,U2,'k')
B1=B1/max(B1);
B2=B2/max(B2);
B3=B3/max(B3);
B4=B4/max(B4);
%plot (f, B1,'b',f,B2,'r'),grid
figure (3)
subplot (2,1,1);
loglog(f,B1,'b',f,B2,'r'),grid
title('')
xlabel ('')
ylabel ('')
subplot (2,1,2);
loglog(f,U1,'g'),grid
title ('')
xlabel ('')
ylabel ('')
figure (4)
subplot (2,1,1);
loglog(f,B3,'b',f,B4,'r'),grid
title('')
xlabel ('')
ylabel ('')
subplot (2,1,2);
loglog(f,U2,'g'),grid
xlabel ('')
ylabel ('')
title ('')