about why in pole placement gives me error?

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azam ghamari
azam ghamari 2018-12-26
评论： oussama sadki 2022-9-5
Hi guys
Does every body knows why in the system :
s=tf('s');
G=(s-2.44)/((s+5)*(s+6)*(s+7));
[A,B,C,D]=tf2ss([1 2.44],[1 18 107 210]);
k_max=1001;
for j=1:k_max
p(j,:)=[-j-1 -3*j -j-2];
K(j,:)=place(A,B,p(j,:));
end
with differeing the p value it gives me this error?
Error using place (line 78)
The "place" command cannot place poles with multiplicity greater than rank(B).
Error in test2 (line 33)
K(j,:)=place(A,B,p(j,:));

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采纳的回答

Aquatris
Aquatris 2018-12-27
It is just the error says. Place command cannot place poles with multiplicity greater than rank(B). In your case, rank(B) is 1. However when j=1, you want to place your poles at [-2 -3 -3]. You see the multiplicity of pole at -3 is 2. So place command cannot be used. If you start j from 2 instead of 1, there won't be an issue.
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Aquatris
Aquatris 2018-12-28
I dont know why you think it does not work. You do realize place is for state feedback not output feedback so you need an observer right?
oussama sadki
oussama sadki 2022-9-5
hello Aquatris, why then rank(B) and each one poles multiplicity should be equal so that feedback gain could be computed, what relationship is there?

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更多回答（1 个）

azam ghamari
azam ghamari 2018-12-28
no, i used it for state feedbackany way when we have somethink like this:
P=p(j,:)=[-j-1 -3*j -j-2];
and B is for example 4x2;
it doesn't work and give me the result.
It gives me this error:
Subscripted assignment dimension mismatch.
Error in test2 (line 31)
K(j,:)=place(A,B,p(j,:));
A=[0.5 0 0.025 0;0 -0.01 0 0.017;0 0 -0.025 0;0 0 0 -0.0178];
B=[0.48 0;0 0.35;0 0.077;0.055 0];
C=[0.5 0 1 0];
D=0;
sys=ss(A,B,C,D);
G=tf(sys)
k_max=1001;
for j=1:k_max
p(j,:)=[-10*rand(1) -20*rand(1) -15*rand(1) -rand(1)];
K(j,:)=place(A,B,p(j,:));
end
  2 个评论
Aquatris
Aquatris 2018-12-28
This error is not because of place function. Just check the size of the matrix place() function return with given A and B matrice and you will realize the error.
Since this is a 2 input 4 state system, place() will return a 2x4 matrix. With the line "K(j,:) = place(...)" you are trying to assign 2x4 matrix to a 1x4 matrix, hence the error dimension mismatch. A quick fix is to change the line to;
K(j,:,:)=place(A,B,p(j,:))

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