[Octave-bug-tracker] [bug #53881] [octave forge] (control) impulse response differs greatly on i386 vs x86_64

[Torsten Lilge]

Follow-up Comment #8, bug #53881 (project octave):

I have realized some numerical problems in imp_invar when it comes o systems
with orders higher than 3 or 4, especially when the system has repeated poles.
I have found a quite simple way to compute the impulse invariant
discretization by firstly using c2d with the 'zoh' method for s*G(s) and
multiplying afterwards with z/z-1 (see comment in help test).

I have attached the new inp_invar.m for testing.

A remark: Matlab and obviously also the impinvar routine in the signal package
assume an impulse of height 1/T for the impulse response. imp_invar is
assuming the unit impulse and therefore returns a discrete-time description
multiplied by 1/T compared to impinvar. This was already the case before my
change and, to my impression, is correct from a control perspective.
Discrete-time systems are not necessarily connected to a sampling time and a
test input 1/T makes no sense for system being discrete-time "by nature".


(file #51643)
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Additional Item Attachment:

File name: imp_invar.m                    Size:4 KB
    <https://file.savannah.gnu.org/file/imp_invar.m?file_id=51643>



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