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[Octave-bug-tracker] [bug #45336] control 2.8.2 - error on MIMO tf multi
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From: |
Lukas Reichlin |
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Subject: |
[Octave-bug-tracker] [bug #45336] control 2.8.2 - error on MIMO tf multiply |
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Date: |
Mon, 22 Jun 2015 11:18:02 +0000 |
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User-agent: |
Mozilla/5.0 (Macintosh; Intel Mac OS X 10_8_5) AppleWebKit/600.6.3 (KHTML, like Gecko) Version/6.2.6 Safari/537.85.15 |
Follow-up Comment #5, bug #45336 (project octave):
The mpower operator for LTI models computes a1^n as n-1 multiplications
(mtimes operator). For MIMO transfer functions, mtimes converts both factors
to state-space, computes the multiplication and then converts the product back
to transfer function. Therefore, mpower computes a3 = a1 * (a1 * a1).
Previously, the conversion of the transfer function to state-space and back
took place during each multiplication:
a3 = tf (ss (a1) * ss (tf (ss (a1) * ss (a1))))
With the patch, the tf -> ss conversion is the first step and the ss -> tf
conversion the last step.
a3 = tf (ss (a1) * (ss (a1) * ss (a1)))
Obviously, the patch doesn't help if you write a1*a1*a1 instead of a1**3
because no tf -> ss -> tf conversion is saved.
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