MATLAB: Subplot function interfering with appropriate plot display

impulse responseplottingsubplot

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)');

Best Answer

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.
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