From: [email protected]
To: [email protected]
Date: Tue, 10 Nov 2009 21:19:49 +0100
CC: [email protected]
Subject: Re: [OctDev] Bugs in control/tzero function (was Re: Discrete
feedback loop)
On 10.11.2009, at 20:32, <[email protected]> <[email protected]> wrote:
> From: [email protected]
> Date: Tue, 10 Nov 2009 09:41:52 +0100
> To: [email protected]; [email protected]
> Subject: [OctDev] Bugs in control/tzero function (was Re: Discrete feedback
> loop)
>
> I made some further investigations (I'm writing pzmap.m for control-oo at the
> moment, which needs to compute the zeros of a system) and came to the
> conclusion that tzero.m from the control package is buggy. The attachment
> contains an example where the discrepancy of the results is big: Matlab gets
> -13.2759, -0.0155, 12.5774, while tzero gets -5.708333, -0.015561, 31.509741.
> Apparently the bug has been undiscovered for about 15 (!) years.
>
> The bad thing is that I reused the code from tzero.m in the control-oo
> package ...
>
> Regards,
> Lukas
>
>
Hi Lukas.
try using tzero2, it works for me on your example. What the difference is I
don't know.
Doug Stewart
Hi Doug,
That's strange. I tried tzero2 on my PPC- as well as on my Intel-Mac and I get
-1 -1 -1 -1 -1 -10That's even worse than tzero, because tzero got at
least one out of three zeros right ;-)
RegardsLukas
octave-3.0.1:1> tzzero
z =
-13.275931
12.577369
-0.015526
and tzzero.m is
A = [ -0.7 -0.0458 -12.2 0
0 -0.014 -0.2904 -0.562
1 -0.0057 -1.4 0
1 0 0 0 ];
B = [ -19.1 -3.1
-0.0119 -0.0096
-0.14 -0.72
0 0 ];
C = [ 0 0 -1 1
0 0 0.733 0 ];
D = [ 0 0
0.0768 0.1134 ];
sys = ss (A, B, C, D);
z = tzero2 (A,B,C,D)
% Expected Results from the "Dark Side"%% -13.2759% 12.5774% -0.0155%%
Results from tzero.m%% -5.708333% -0.015561% 31.509741
So I don't know why you are getting a different answer.
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