书上抄的程序为什么运行就有错啊？
M=20;alpha=(M-1)/2;l=0;w1=(2*pi/M)*l;
Hrs=[1,1,1,zeros(1,15),1,1];
Hdr=[1,1,0,0];wdl=[0,0.25,0.25,1];
k1=0:floor((M-1)/2);k2=floor((M-1)/2)+1:M-1;
angH=[-alpha*(2*pi)/M*k1,alpha*(2*pi)/M*(M-k2)];
H=Hrs.*exp(j*angH);
h=real(ifft(H,M));
[db,mag,pha,grd,w]=freqz_m(h,[1]);
[Hr,ww,a,L]=Hr_Type2(h);
subplot(1,1,1)
subplot(2,2,1);plot(w1(1:11),'0',wdl,Hdr);
axis([0,1,-0.1,1.1]);title('Frequency Samples:M=20');
xlabel('frequnecy in pi units');ylabel('Hr(k)')
set(gca,'XTickMode','manual','XTick',[0,0.2,0.3,1]);
set(gca,'YTickMode','manual','YTick',[0,1]);grid
subplot(2,2,2);stem(1,h);axis([-1,M,-0.1,0.3]);
title('Impulse Response');xlabel('n');ylabel('h(n)')
xa=0.*1;
hold on
plot(1,xa,'k');
hold off
subplot(2,2,3);plot(ww/pi,Hr,w1(1:11)/pi,Hrs(1;11),'0');
axis([0,1,-0.2,1.2]);title('Amplitude Response')
set(gca,'XTickMode','manual','XTick',[0,0.2,0.3,1]);
set(gca,'YTickMode','manual','YTick',[0,1]);grid
subplot(2,2,4);plot(w/pi,db);axis([0,1,-60,10]);
title('Magnitude Response');xlabel('frequnexcy in pi units');ylabel('Decibels');
set(gca,'XTickMode','manual','XTick',[0,0.2,0.3,1]);
set(gca,'YTickMode','manual','YTick',[-16,0]);grid
set(gca,'YTickLabeMode','manual','YTickLabels',['16';'0'])