tf2ss discrepancy

[Julius Smith]

I just encountered the following difference between Octave and Matlab:

OCTAVE:

octave:6> [A,B,C,D] = tf2ss([1 2 3], [1 1/2 1/3])
A =

   1.1102e-16   3.3333e-01
  -1.0000e+00  -5.0000e-01

B =

  -2.6667
   1.5000

C =

   0   1

D =  1

octave:7> which tf2ss
'tf2ss' is a function from the file /Users/me/octave/signal-1.3.0/tf2ss.m

MATLAB:

>>  [A,B,C,D] = tf2ss([1 2 3], [1 1/2 1/3])

A =

   -0.5000   -0.3333
    1.0000         0


B =

     1
     0


C =

    1.5000    2.6667


D =

     1

Both appear to be valid state-space models (ss2tf gives back the 
original in both cases).



Julius O. Smith III <address@hidden>
Professor of Music and, by courtesy, Electrical Engineering
CCRMA, Stanford University
http://ccrma.stanford.edu/~jos/