Re: Request for Matlab output

[Steph Bredenhann]

On 29/10/2015 21:13, Lukas Reichlin wrote:
> On 29.10.2015, at 18:50, Lukas Reichlin <address@hidden> wrote:
> > > On 29.10.2015, at 12:36, Lukas Reichlin <address@hidden> wrote:
> > >
> > > Dear Octave community,
> > >
> > > In order to improve error handling in the control package, I would like to know 
> > > what Matlab’s output/error message looks like for each of the following three 
> > > lines of code:
> > >
> > > dss (1, 2, 3, 4, 0)
> > >
> > > feedback (tf (1), tf (-1))
> > >
> > > feedback (ss (1), ss (-1))
> > >
> > > Could someone with access to Matlab and its Control System Toolbox please send 
> > > me the resulting text output?
> > >
> > > Thanks in advance,
> > > Lukas
> > Gentlemen, thank you very much for your help! I’ve just pushed a file 
> > containing my conclusions:
> >
> > http://sourceforge.net/p/octave/control/ci/default/tree/devel/algebraic_loops.m
> >
> > Best regards,
> > Lukas
> May I ask you for another test in Matlab?
>
>
> e = zeros (2, 2);
> a = [-1, 1; 1, -1];
> b = [1; 0];
> c = [1, 0];
> d = 0;
> sys = dss (a, b, c, d, e)
> G = tf (sys)
> H = zpk (sys)
>
>
> I think that descriptor systems with all-zero E matrix and non-invertible A 
> matrix are invalid. Now I wonder whether Matlab accepts those systems at all or 
> only returns NaN’s later on.
>
> Best regards,
> Lukas
Ubuntu 14.04 x64 with Matlab 2015b


sys =

  a =
       x1  x2
   x1  -1   1
   x2   1  -1

  b =
       u1
   x1   1
   x2   0

  c =
       x1  x2
   y1   1   0

  d =
       u1
   y1   0

  e =
       x1  x2
   x1   0   0
   x2   0   0

Continuous-time state-space model.

Warning: The frequency response has poor relative accuracy. This may be 
because the
response is nearly zero or infinite at all frequencies, or because the 
state-space
realization is ill conditioned. Use the "prescale" command to 
investigate further.
> In ltipack.ssdata/iodynamics
  In ltipack.ssdata/zpk (line 23)
  In ltipack.ssdata/tf (line 20)
  In lti/tf_ (line 283)
  In DynamicSystem/tf (line 90)
  In untitled (line 11)

G =

  -6369051672525772

Static gain.

Warning: The frequency response has poor relative accuracy. This may be 
because the
response is nearly zero or infinite at all frequencies, or because the 
state-space
realization is ill conditioned. Use the "prescale" command to 
investigate further.
> In ltipack.ssdata/iodynamics
  In ltipack.ssdata/zpk (line 23)
  In lti/zpk_ (line 295)
  In DynamicSystem/zpk (line 80)
  In untitled (line 12)

H =

  -6.3691e+15

Static gain.

>>