% Figure 6.17  demonstration of time varying impulse response

N=20;
h=zeros(N,4);
figure;
for j=1:4
    t=ones(N,1);
a=randn(N,1);
a=abs(a)/max(abs(a));
a=fliplr(sort(a'));
test=ceil(rand(6,1)*N);
test=sort(test);
a=a';

h(test,j)=a(test);
line(
end
[M,N]=size(h);
x=[1:N];
y=[1:M];
[X,Y]=meshgrid(x,y);
figure;
plot3(X,Y,h,'k')
%stem3(h,'k')
set(gca,'ydir','reverse')