% 程序名：example2_3.m
clear;close all
n0=-25;
n1=25;
t=n0:n1;
x=0.5.^(t).*u(t);
h=u(t);
y=conv(x,h);%卷積計(jì)算
%將卷積的結(jié)果取得和兩個(gè)輸入的信號一樣長，以便在相同的坐標(biāo)中繪制其圖形并方便比較。
l=length(y);
m=2*n0:n0-1;
n=n1+1:2*n1;
m1=zeros(1,abs(n0));
p1=zeros(1,abs(n1));
lm=length(m1);
ln=length(p1);
y=y([lm+1:l-ln]);
c=u(-t);
%計(jì)算移位長度
hl=u(-t-15);
c=u(-t-15);
l=length(hl);
%以下程序繪制激勵(lì)信號和系統(tǒng)沖激響應(yīng)的波形
clf;
subplot(4,2,1);stem(t,x,'.');hold on;axis([-10,10,0,1.5])
subplot(4,2,2);
stem(t,h,'r.');hold on;axis([-10,10,0,1.5])
%下段程序?qū)崿F(xiàn)移位動(dòng)畫
b=31;
for i=1:b
    for j=l-1:-1:1
        hl(j+1)=hl(j);
        c(j+1)=c(j);
    end
    c(1)=1;
    hl(1)=1;    
    subplot(4,1,3);
    stem(t,hl,'r.'); axis([-15,15,0,1.5])
    subplot(4,1,2);stem(t,x,'.');axis([-15,15,0,1.5])
    hold off;
    subplot(4,1,4);
    stem(t,c.*y,'r.');axis([-15,15,0,2.5]);    
    pause;
end