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Help with RootLocusPlot

  • To: mathgroup at smc.vnet.net
  • Subject: [mg129022] Help with RootLocusPlot
  • From: <emammendes at gmail.com>
  • Date: Sun, 9 Dec 2012 10:57:32 -0500 (EST)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • Delivered-to: l-mathgroup@wolfram.com
  • Delivered-to: mathgroup-newout@smc.vnet.net
  • Delivered-to: mathgroup-newsend@smc.vnet.net

Hello all

 

I am experiencing some problems when using the command RootLocusPlot.  Here
is what I need to do

 

tf[s_,\[Alpha]_,k_]:=k (s+\[Alpha])^3/(s^2-2 s+2)^2;tf[s,\[Alpha],k]

 

RootLocusPlot[tf[s,2,k],{k,0,20000},PlotRange->{{-12,2},{-8,8}},Method->"NDS
olve",PlotPoints->1000]

 

First of all, the whole thing takes quite some time to finish, but worse
part is not that, the result gives the false impression that the real Root
Locus is what is shown on the screen. It is not!

 

M***B takes a second to do the same thing and returns the real thing!  

 

I have changed the number of points, the range of k and etc. 

 

What am I doing wrong?  Is there a way of setting specific values of k
(something like logspace in M***B)?  

 

Many thanks

 

Ed

 



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