[Octave-bug-tracker] [bug #66651] control package, MIMO systems wrong created C matrix for state space representation using ss

[Torsten Lilge]

Update of bug #66651 (group octave):

                  Status:                    None => Need Info

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Follow-up Comment #2:

There exists an indefinite number of state space representations with
identical transfer function. You are expecting a diagonal form. You can try to
transform the result of ss() into a diagonal form by 

# Similarity trnasformation
[T, lambda] = eig (sys_ss.a);
A = inv(T)*sys_ss.a*T;
B = inv(T)*sys_ss.b;
C = sys_ss.c*T;
# Set very small values to 0 (finite
# numerical accuracy) for a nicer output
A(abs(A)<1e-12)= 0
B(abs(B)<1e-12)= 0
C(abs(C)<1e-12)= 0

However, this method is only possible for systems with single eigenvalues.

Could you please try this and report back whether you get the expected
results? The order of non-zero entries in B and C might differ because the
order of the subsystems in A follows the magnitude of their eigenvalues.


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