f 1 = sin( 10 * pi * t)+sin( 100 * pi * t)+sin(200 * pi * t)；

F2 = sin(200 * pi * t)+sin( 10 * pi * t)-sin( 100 * pi * t)；

Figure (1);

plot(t，f 1，t，F2)；

Figure (2);

t = 1000 *( 1:5 12)/ 1024；

ff 1=fft(f 1， 1024)/ 1024；

dff 1 = 2 * ABS(ff 1( 1:5 12))；

ff2=fft(f2， 1024)/ 1024；

dff 2 = 2 * ABS(ff2( 1:5 12))；

plot(t，dff 1，t，dff 2)；

When selecting the sampling frequency, pay attention to the sampling law and the period of the waveform (the sampling frequency is not less than 200Hz and the period is not less than 0.2s).