IMPULSE  Impulse response of LTI models.
 
    IMPULSE(SYS) plots the impulse response of the LTI model SYS (created 
    with either TF, ZPK, or SS).  For multi-input models, independent
    impulse commands are applied to each input channel.  The time 
    range and number of points are chosen automatically.  For continuous 
    systems with direct feedthrough, the infinite pulse at t=0 is 
    disregarded.
 
    IMPULSE(SYS,TFINAL) simulates the impulse response from t=0 to the 
    final time t=TFINAL.  For discrete-time systems with unspecified 
    sampling time, TFINAL is interpreted as the number of samples.
 
    IMPULSE(SYS,T) uses the user-supplied time vector T for simulation. 
    For discrete-time models, T should be of the form  Ti:Ts:Tf  
    where Ts is the sample time.  For continuous-time models, 
    T should be of the form  Ti:dt:Tf  where dt will become the sample 
    time of a discrete approximation to the continuous system.  The
    impulse is always assumed to arise at t=0 (regardless of Ti).
 
    IMPULSE(SYS1,SYS2,...,T) plots the step response of multiple
    LTI models SYS1,SYS2,... on a single plot.  The time vector T is 
    optional.  You can also specify a color, line style, and marker 
    for each system, as in  
       impulse(sys1,'r',sys2,'y--',sys3,'gx').
 
    When invoked with left-hand arguments,
       [Y,T] = IMPULSE(SYS) 
    returns the output response Y and the time vector T used for 
    simulation.  No plot is drawn on the screen.  If SYS has NY
    outputs and NU inputs, and LT=length(T), Y is an array of size
    [LT NY NU] where Y(:,:,j) gives the impulse response of the 
    j-th input channel.
 
    For state-space models, 
       [Y,T,X] = IMPULSE(SYS, ...) 
    also returns the state trajectory X which is an LT-by-NX-by-NU 
    array if SYS has NX states.