ex020200.m

《数字信号处理及其MATLAB实现》程序集(2004)

% Chapter 02: Example 02.02: 信号合成
%
figure(1); clf
n = -2:10; x = [1:7,6:-1:1];
% a) x1(n) = 2*x(n-5) - 3*x(n+4)
[x11,n11] = sigshift(x,n,5); [x12,n12] = sigshift(x,n,-4);
[x1,n1] = sigadd(2*x11,n11,-3*x12,n12);
subplot(2,1,1); stem(n1,x1); title('例2.2a的序列')
text(max(n1)+2,min(x1)-1,'n');
ylabel('x1(n)'); axis([min(n1)-1,max(n1)+1,min(x1)-1,max(x1)+1])
set(gca,'XTickMode','manual','XTick',[min(n1),0,max(n1)])
%
% b) x2(n) = x(3-n) + x(n)*x(n-2)
[x21,n21] = sigfold(x,n); [x21,n21] = sigshift(x21,n21,3);
[x22,n22] = sigshift(x,n,2); [x22,n22] = sigmult(x,n,x22,n22);
[x2,n2] = sigadd(x21,n21,x22,n22);
subplot(2,1,2); stem(n2,x2); title('例2.2b的序列')
text(max(n2)+2,0,'n');
ylabel('x2(n)'); axis([min(n2)-1,max(n2)+1,0,40])
set(gca,'XTickMode','manual','XTick',[min(n2),0,max(n2)])