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Re: Root locus figure is bad plotted


From: Torsten
Subject: Re: Root locus figure is bad plotted
Date: Fri, 20 Apr 2018 07:09:19 +0200

On 19.04.2018 17:26, Beginner1 wrote:
>  
> Hi Doug, 
> 
> Thank you for the answer. However in that example I simplified a bit my code
> and actually the NUM and DEN polynomials are generated via this command:
> [NUM,DEN]=ss2tf(sys.a,sys.b,sys.c,sys.d);
> 
> Therefore, there are NUM and DEN functions whose representation is
> calculated by Octave and Octave gives for example the negative [-15,-300]
> representation instead of [15,300]. And this is an iterative process where
> there are at least 100 NUM and DEN polynomial functions...
> 
> So is there another way to make the rlocus plot work properly?
> 
> Thank you
> 

For your case, i.e. negative gain of the system, the shown root locus is
correct. The negative gain together with the negative feedback of the
closed loop results in a positive feedback.

Torsten



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