%% ------------------------------------------------------------------------

%%            Output Info about this m-file

fprintf('\n***********************************************************\n');

fprintf('        <DSP using MATLAB> Problem 2.16 \n\n');

banner();

%% ------------------------------------------------------------------------

%% ------------------------------------------------------

%%              sequence of 51 samples

%% ------------------------------------------------------

nx1 = [-1:49]; x1 = (0.8 .^ nx1) .* stepseq(0, -1, 49);

nh1 = [-1:49]; h1 = ( (-0.9).^nh1 ) .* stepseq(0, -1, 49);

[y1, ny1] = conv_m(x1, nx1, h1, nh1);

figure('NumberTitle', 'off', 'Name', 'Problem 2.16')

set(gcf,'Color',[1,1,1])                  % 改变坐标外围背景颜色

subplot(3,1,1); stem(nx1, x1); title('x1 sequence');

xlabel('n'); ylabel('x(n)') ;

grid on

subplot(3,1,2); stem(nh1, h1); title('h1 sequence');

xlabel('n'); ylabel('h1(n)');

grid on;

subplot(3,1,3); stem(ny1, y1); title('y1=x1*h1 sequence');

xlabel('n'); ylabel('y1(n)');

grid on;

%% -----------------------------------------------------

%%         Trancate to 26 samples

%% -----------------------------------------------------

nx2 = [-1:24]; x2 = (0.8 .^ nx2) .* stepseq(0, -1, 24);

nh2 = [-1:24]; h2 = ( (-0.9).^nh2 ) .* stepseq(0, -1, 24);

[y2, ny2] = conv_m(x2, nx2, h2, nh2);

figure('NumberTitle', 'off', 'Name', 'Problem 2.16')

set(gcf,'Color',[1,1,1])                  % 改变坐标外围背景颜色

subplot(3,1,1); stem(nx2, x2); title('x2 sequence');

xlabel('n'); ylabel('x2(n)') ;

grid on

subplot(3,1,2); stem(nh2, h2); title('h2 sequence');

xlabel('n'); ylabel('h2(n)');

grid on;

subplot(3,1,3); stem(ny2, y2); title('y2=x2*h2 sequence');

xlabel('n'); ylabel('y2(n)');

grid on;

%% ----------------------------------------------------------

%%            filter function

%% ----------------------------------------------------------

b = [1]; a = [1, 0.9];

y3 = filter(b, a, x1);

figure('NumberTitle', 'off', 'Name', 'Problem 2.16')

set(gcf,'Color',[1,1,1])                  % 改变坐标外围背景颜色

%subplot(3,1,3);

stem(nx1, y3); title('y3 sequence');

xlabel('n'); ylabel('y3(n)');

grid on;