%濾波器 
[Lo_D,Hi_D,Lo_R,Hi_R] = wfilters('coif3'); 
subplot(2,2,1); 
stem(Lo_D);grid; 
title('(a)') 
subplot(2,2,2); 
stem(Lo_R);grid; 
title('(c)') 
subplot(2,2,3); 
stem(Hi_D);grid; 
title('(b)') 
subplot(2,2,4); 
stem(Hi_R);grid; 
title('(d)4')