Tue 16 Jun 2015 09:26:08 PM UTC, original submission:
using control-2.8.1. performing a multiple MIMO tf multiplication produces erroneous output. (haven't checked this under 2.8.2, as that version produces a different error)
using a simple 2x2 tf, the following commands reproduce the problem:
a2 calculates as expected, and a minreal(a2) produces the expected minimized form. the a3 and a4 results get huge, and then the a5 result drops and zeros out almost all of the numerator coefficients. using minreal between multiplies for a3, a4 and a5 make little difference.
As the output gets messy, I attached a text file of the Octave output with and without minreal.
Note that the order of multiplication (whether it's a1* or *a1) in the definition of a2-a5 seems to matter on whether the coefficients match the expected analytical result, but it produces zeros on a5.
Checking Matlab output for the same (ML 2015a) produces sensible results, although as expected they don't minimize as nicely as Maxima. A minreal between multiply steps gets it fairly close through a4.
I attached a png of a maxima output showing what the minimized output of those should be. granted I expect Maxima to be better at handling the higher order polynomials.
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