卷积满足
1° 交换律 f1(t) *f2(t)=f2(t) *f1(t);
2° 结合律 [f1(t) *f2(t)] *f3(t)=f1(t)*[f2(t)*f3(t)] ;
3° 分配律 f1(t)*[f2(t)+f3(t)]=f1(t)*f2(t)+f1(t)*f3(t).
