小波去噪matlab的代码，%用db1小波对原始信号进行3层分解并提取系数[c,l]=wavedec(s,3,'db1');a3=appcoef(c,l,'db1',3);d3=detcoef(c,l,3);d2=detcoef(c,l,2);d1=detcoef(c,l,1);thr=1;