lsim vs. filter for simulation in Octave 2.1.50

[E. Joshua Rigler]

Please, don't hesitate to tell me *why* this is a dumb question...

If I have numerator and denominator filter coefficients:

 A = [1.0  .33]
 B = [0.2  .10]
 lag = [0 1] ;; not necessary for anything


...or if I have a system derived from a state-space description with:


 A = -.33
 B = .10
 C = 1
 D = 0.2
 sys = ss2sys (A,B,C,D,1,0,1)


...shouldn't I get the same output from:


 1) filter (B,A,[1;zeros(9,1)])
...and...
 2) lsim (sys,[1;zeros(9,1)],[1:10])


It seems that the feedthrough term in the system structure (D*u) is not
incorporated into the updated state properly by lsim, but maybe my
concept of what is "proper" is flawed.

-EJR



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