代码：

%% ----------------------------------------------------------------------------%%            Output Info about this m-filefprintf('\n***********************************************************\n');fprintf('        
     
       Problem 4.9 \n\n');banner();%% ----------------------------------------------------------------------------%% -------------------------------------------------%%            1      X(z)%% -------------------------------------------------b1 = [1, -2, 3, -4]; nb1 = [0:3]; a1 = [4, 3, -2, 1]; na1 = [0:3];               %  [x1, nx1] = conv_m(b1, nb1, a1, na1)figure('NumberTitle', 'off', 'Name', 'Problem 4.9.1 X1(z)')set(gcf,'Color','white'); stem(nx1, x1);title('X1'); grid on;%% -------------------------------------------------%%            2      X(z)%% -------------------------------------------------b2 = [1, -2, 3, 2, 1]; nb2 = [-2:2]; a2 = [1, 0, 0, 0, 0, 0, -1]; na2 = [-3:3];               %  [x2, nx2] = conv_m(b2, nb2, a2, na2)figure('NumberTitle', 'off', 'Name', 'Problem 4.9.2 X2(z)')set(gcf,'Color','white'); stem(nx2, x2);title('X2'); grid on;%% -------------------------------------------------%%            3      X(z)%% -------------------------------------------------b3 = [1, 1, 1]; nb3 = [0:2];                %  [x3_1, nx3_1] = conv_m(b3, nb3, b3, nb3);[x3, nx3] = conv_m(x3_1, nx3_1, b3, nb3)figure('NumberTitle', 'off', 'Name', 'Problem 4.9.3 X3(z)')set(gcf,'Color','white'); stem(nx3, x3);title('X3'); grid on;%% -------------------------------------------------%%            4      X4(z)=X1(z)X2(z)+X3(z)%% -------------------------------------------------[x4_1, nx4_1] = conv_m(x1, nx1, x2, nx2);[x4, nx4] = sigadd(x4_1, nx4_1, x3, nx3)figure('NumberTitle', 'off', 'Name', 'Problem 4.9.4 X4(z)')set(gcf,'Color','white'); stem(nx4, x4);title('X4'); grid on;%% -------------------------------------------------%%            5      X(z)%% -------------------------------------------------b5 = [1, 0, -3, 0, 2, 0, 5, 0, -1]; nb5 = [1:9]; a5 = [4, 2, 3, 1]; na5 = [-4:-1];               %  [x5, nx5] = conv_m(b5, nb5, a5, na5)figure('NumberTitle', 'off', 'Name', 'Problem 4.9.5 X5(z)')set(gcf,'Color','white'); stem(nx5, x5);title('X5'); grid on;
     

　　运行结果：