Error using place (line 78) The "place" command cannot place poles with multiplicity greater than rank(B). what is this error?

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mani zarouri 2018-11-1

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评论： mani zarouri 2023-5-19

I used to have no issues with this back when I used Matlab 2017b but now I can't get the pole placement function to work. here is what I got:

>> syms k1 k2 k3 s
>> A
A =
            0   1.0000e+00            0
            0            0   1.0000e+00
  -5.0160e-04  -1.2880e-01  -8.5400e-01
>> B
B =
     1
     0
     0
>> Ac
Ac =
[                                   -K1,    1 - K2,      -K3]
[                                     0,         0,        1]
[ -1156610853421589/2305843009213693952, -161/1250, -427/500]
>> clpoles=[-1/2 -1/15 -1/15];
>> Dc=collect(det(s*eye(3)-Ac));
>> K=place(A,B,clpoles)
*Error using place (line 78)
The "place" command cannot place poles with multiplicity greater than rank(B).*

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mani zarouri 2023-5-19

编辑：mani zarouri 2023-5-19

Actually the issue was that the Matrix B was incorrect. It is supposed to be a 3x1 matrix with values in the order below: B= [0;0;1] This resolved the issue.

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Answer 1

mani zarouri 2023-5-19

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Actually the issue was that the Matrix B was incorrect. It is supposed to be a 3x1 matrix with values in the order below: B= [0;0;1] This resolved the issue.

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Answer 2

Siddharth Jawahar 2023-5-19

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Hi Mani,

This is not a bug, this is a limitation as spelled out in the error message. You cannot specify pole locations with multiplicity greater than rank(B)=1 in this example. Since closed-loop poles (-1/15,-1/15) has multiplicity 2, your target location violates this requirement. In general it's not a good idea to place poles at the same location because such a configuration is very sensitive to perturbations.

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mani zarouri 2023-5-19

Thank you for your answer. I learned something new regarding the consequence of placing poles at the same location. Although, the answer to the question was with how the matrix B was setup.

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