matlab

n=0:0.01:2;for i=1:4switch i    case 1 ,N=2;  %频率点    case 2 ,N=5;  %取4种滤波器    case 3,N=10;    case 4,N=20;end[z,p,k] =buttap ( N );        %设计butterworth滤波器[b,a] = zp2tf(z,p,k);          %将零点、极点、增益的形式转换为传递函数[H,w] =freqs(b,a,n);         %按n制定的频率点给出频率响应magH2 = (abs(H)).^2;       %给出传递函数幅度平方hold on;plot (w, magH2);                endxlabel ('w/wc');ylabel('|H(jw)|^2');title('Butterworth');text(1.5,0.18,'n=2');text(1.3,0.08,'n=10');text(1.16,0.08,'n=10');text(0.93,0.98,'n=20');grid on;