《DSP using MATLAB》Problem 2.9

代码：

%% ------------------------------------------------------------------------
%%            Output Info about this m-file
fprintf('\n***********************************************************\n');
fprintf('        <DSP using MATLAB> Problem 2.9 \n\n');

banner();
%% ------------------------------------------------------------------------

nx = [0:1:20]; 
 x = 0.9 .^ nx;

ny = [-20:1:0];
 y = 0.8 .^ (-ny); 

figure('NumberTitle', 'off', 'Name', 'Problem 2.9')
set(gcf,'Color',[1,1,1])                  % 改变坐标外围背景颜色

subplot(2,1,1); stem(nx, x); title('x sequence');
xlabel('n'); ylabel('x(n)') ;
grid on
subplot(2,1,2); stem(ny, y); title('y sequence');
xlabel('n'); ylabel('y(m)');
grid on;


[x1, nx1] = sigfold(x, nx);           % obtain x(-n)
[y1, ny1] = sigfold(y, ny);

[Rxy, nxy] = conv_m(x1, nx1, y, ny);
[Rxx, nxx] = conv_m(x1, nx1, x, nx);


figure('NumberTitle', 'off', 'Name', 'Problem 2.9')
set(gcf,'Color',[1,1,1])                  % 改变坐标外围背景颜色

subplot(2,1,1); stem(nxy, Rxy); title('Crosscorrelation Rxy(l) sequence');
xlabel('nxy'); ylabel('Rxy(nxy)') ;
grid on
subplot(2,1,2); stem(nxx, Rxx); title('Autocorrelation Rxx(l) sequence');
xlabel('nxx'); ylabel('Rxx(nxx)');
grid on;

　　

　　运行结果：