Matlab Dimpulse function documentaion not found

I was using the dimpulse function in one ofthe codes for digital signal processing. It is working properly. But I couldn't find the documentaion for the function. Here is my code:

n=0:10; 
% impulse response of first order system
% y(n)-0.9*y(n-1)=2*x(n)
b=[2 0 0]; 
a=[1 -0.9 0]; 
y=dimpulse(b,a,length(n)); 
subplot(2,1,1);
stem(n,y); 
xlabel('n--->');
ylabel('amplitude');
title('impulse response of first order system'); 
% impulse response of second order system
% y(n)+0.6*y(n-1)+0.8*y(n-2)=x(n) 
b=[1 0 0];
a=[1 0.6 0.8];
y1=dimpulse(b,a,length(n));
subplot(2,1,2);
stem(n,y1); 
xlabel('n---->'); 
ylabel('amplitude');
title('impulse response of second order system');

Answer 1

[John D'Errico]

It seems dimpulse (or at least one version thereof) can be found in the control TB.

which dimpulse -all

/MATLAB/toolbox/control/ctrlobsolete/dimpulse.m

However, given the location, my guess is it may be considered obsolete. As such, the docs for dimpulse may be missing.

And there are also at least a few universities who have written their own version of dimpulse.

But the help for dimpulse (the control TB version) can be found as:

help dimpulse

 DIMPULSE Impulse response of discrete-time linear systems.
     DIMPULSE(A,B,C,D,IU)  plots the response of the discrete system:
 
        x[n+1] = Ax[n] + Bu[n]
        y[n]   = Cx[n] + Du[n]
 
    to an unit sample applied to the inputs IU.  The number of
    points is determined automatically.
 
    DIMPULSE(NUM,DEN) plots the impulse response of the polynomial
    transfer function  G(z) = NUM(z)/DEN(z)  where NUM and DEN contain
    the polynomial coefficients in descending powers of z.
 
    DIMPULSE(A,B,C,D,IU,N) or DIMPULSE(NUM,DEN,N) uses the user-
    supplied number of points, N.  When invoked with left hand 
    arguments,
        [Y,X] = DIMPULSE(A,B,C,D,...)
        [Y,X] = DIMPULSE(NUM,DEN,...)
    returns the output and state time history in the matrices Y and X.
    No plot is drawn on the screen.  Y has as many columns as there 
    are outputs and X has as many columns as there are states.
 
    See also  IMPULSE, STEP, INITIAL, LSIM.

Answer 2

[Sam Chak]

Hi @Md. Ikrama Hossain

For your information, the current version of the impulse() function can be applied to both continuous-time and discrete-time LTI models generated using the tf(), zpk(), or ss() commands.

A   = [1.6 -0.7;
       1.0  0.0];
B   = [0.5; 
       0.0];
C   = [0.1 0.1];
D   =  0.0;
Ts  =  0.2;     % sampling time
sys = ss(A, B, C, D, Ts);
impulse(sys), grid on

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