%本程序用來計(jì)算并演示兩個(gè)信號(hào)之間的卷積的動(dòng)畫效果  程序名：example2_4.m
clear;close all
n0=-15;
n1=15;
t=n0:n1;
h=1.2.^(t).*(u(t)-u(t-7));
x=u(t)-u(t-5);
f=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(hào)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(f);
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);
f=f([lm+1:l-ln]);
c=u(-t);
%計(jì)算移位長度
hl=fliplr(h);
l=length(hl);
k0=min(find(hl))+length(find(hl));
v0=min(find(f));
w0=min(find(x));
if k0<=w0
    q=3;
else
    q=k0-w0+5;
end
for i=1:q
    y=hl(1);
    for j=1:l-1
        hl(j)=hl(j+1);c(j)=c(j+1);
    end
    hl(l)=y;c(l)=0;
end
%以下程序繪制激勵(lì)信號(hào)和系統(tǒng)沖激響應(yīng)的波形
clf;
subplot(4,2,1);stem(t,x,'.');hold on;axis([-10,10,0,3.5])
subplot(4,2,2);
stem(t,h,'r.');hold on;axis([-10,10,0,3.5])
%下段程序?qū)崿F(xiàn)移位動(dòng)畫
b=q+length(find(f));
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)=0;    
    subplot(4,1,3);
    stem(t,hl,'r.'); 
    subplot(4,1,2);stem(t,x,'.');
    hold off;
    subplot(4,1,4);
    stem(t,c.*f,'r.');axis([n0,n1,min(f),max(f)]);    
    pause;
end