Subplot function interfering with appropriate plot display

When I try to use subplot to show impulse response and unit step response in the same figure, the impulse response plot displays incorrectly. Any idea why subplot is not plotting both the impulse response and unit step response appropriately? Uncomment the second section of code to see the problem. Thanks!

a = [1,-1,0.9]; 
  b = [1];
  n = [-20:120];
  h = impz(b,a,n);
  subplot(1,2,1); stem(n,h);
  title('Impulse response'); xlabel('n'); ylabel('h(n)');

    % %Plot unit step response ex. 2.11 b
    % x = stepseq(0,-20,120);
    % a1 = [1,-1,0.9]; b1 = [1];
    % s = filter(b1,a1,x);
    % n1 = [-20:120];
    % subplot(1,2,2); stem(n1,s);
    % title('Step response'); xlabel('n'); ylabel('s(n)');

[Adam]

I can't run the code as I have no idea what stepseq is. Saying something 'displays incorrectly' is not very useful though. Please explain what is incorrect or attach a picture showing it.

Answer 1

[Star Strider]

The impulse and step responses are defined as beginning from 0, and do not exist for negative time. I can’t find ‘stepseq’ in the online documentation.

This works:

a = [1,-1,0.9];
b = [1];
n = [-20:120];
[h,t] = impz(b,a,n);
subplot(1,2,1); stem(t,h);
title('Impulse response'); xlabel('n'); ylabel('h(n)');

%Plot unit step response ex. 2.11 b
% x = stepseq(0,-20,120);
a1 = [1,-1,0.9]; b1 = [1];
s = stepz(b1,a1,120);
n1 = [-20:120];
subplot(1,2,2); stem(n1',[zeros(21,1); s]);
title('Step response'); xlabel('n'); ylabel('s(n)');

I would also stack them vertically rather than plot them horizontally, so use subplot(2,1,1) and subplot(2,1,2) instead.

[abbz123]

Awesome. Thank you so much!

[Star Strider]

As always, my pleasure!

Answer 2

[Siambou Camara]

A well-known discontinuous function is impulse function that is defined as: δ(t) = 1 t = 0 0 otherwise. (1) In order to generate impulse function using matlab, follow the same steps as previous section, but this time using the following Matlab code.