w=0:1/100:1;
load db2;z=db2
subplot(421);stem(z);
s=[exp(0*w) ;exp(2*pi*i*w); exp(2*2*pi*i*w); exp(3*2*pi*i*w);];
k=z*s;
subplot(422);plot(w,real(k));

C = [z(1)  0  0
     z(3)  z(2)  z(1)
     0      z(4) z(3) ]
[V,D]=eig(-2*C)

ph= [ V(1,2) V(2,2) V(3,2) 0 ];
x=0:1/1:3;
subplot(423);plot(x,ph);

x1=0:1/2:3;


PH=zeros(1,7);
PH(1:2:8)=ph(1:4);
conv(2*z,ph)
PH(2:2:7)=ans(2:2:7);
subplot(424);plot(x1,PH);