From help-octave-request at bevo dot che dot wisc dot edu  Thu Oct 23 12:17:24 1997
Subject: Re: [SUGGESTIONS] for OCST (perhaps I'm wrong)
From: Kai Mueller <mueller at ifr dot ing dot tu-bs dot de>
To: "A. Scottedward Hodel" <A dot S dot Hodel at eng dot auburn dot edu>
Cc: help-octave at bevo dot che dot wisc dot edu
Date: Thu, 23 Oct 1997 18:15:26 +0100

On Thu, Oct 23, 1997 at 10:45:25AM -0500, A. Scottedward Hodel wrote:
> [name deleted]
> > 
> >         Hi
> > 
> >         I'm a guy who had to work with MatLab and preferred free
> > software, so I started to surf with Octave. I also had to use the
> > control package; initially I used Matlab's, until I found trouble, and
> > then someone recommended me to use the OCST snapshots (which I didn't
> > know, BTW :).
> > 
> >         Ok, as it says this is work in progress, I'm reporting some
> > slight differences I've noticed; if you already know them, sorry for
> > being repetitive :)
> > 
> >         ss2zp() admits an IU argument at MatLab's package. Not a guru,
> >                 so no idea on what it means, though it could be Input
> >                 Unit, or In Utero or ...
> > 
> >         impulse() at Matlab also admits another set of arguments,
> >                   being the system's state variables, the IU (still
> >                   don't know what it it) and a time vector. Perhaps
> >                   the form you offer and the one I need are easily
> >                   calculated one from another, but not for the
> >                   rookie. Then it'd just be a compatibility issue.
> > 
[remaining text deleted]

Some remarks to impulse() [the same applies to step()]
and Matlab 4.x Control System Toolbox:

 o the data structure "sys" to represent a dynamic system
   did not exist in the Matlab 4.x CSTB.
   The packed system approach in the Mu-Tools can be regarded
   of a subset of the OCST system data structure. Therefore,
   the arguments canot be compatible with Matlab.

 o No attempt was made be compatible with Matlab's impulse().
   "impulse(jet707)" for example, is short and powerful.

 o OCST impulse() is equivalent to Matlab impulse() and dimpulse().
   The argument list ist shorter and OCST impulse() knows about
   sampling time, input and output names from the system
   data structure.

 o The parameter "inp" is the same as "IU" in Matlab (the input number).

 o OCST impulse() tries to estimate as much as possible.
   impulse() does not accept an "equally spaced time vector"
   as in Matlab. The parameter "tstop" is simply a scalar value.
   This allows impulse to estimate the step size automatically
   if the system is continuous.
   To plot the first 5 seconds of a systems impulse response 
      "impulse(sys, 1, 5)"
   in OCST is considered to be easier to use (and safer) than
     "t=linspace(0,5,200);  impulse(a,b,c,d,1,t);"
   If you really *need* 200 data point you can specify
     "impulse(sys,1,5,200)".

-- 
 Kai P. Mueller
 Control Department (Regelungstechnik) | Phone [+49] (531) 391-3835
 Technical University Braunschweig     | Fax   [+49] (531) 391-5194
 D-38092 Braunschweig                  | Email mueller at ifr dot ing dot tu-bs dot de