Unable to perform assignment because the left and right sides have a different number of elements.

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jana nassereddine 2023-5-22

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1970209-unable-to-perform-assignment-because-the-left-and-right-sides-have-a-different-number-of-elements

回答： Askic V 2023-5-22

Hello everyone, so I have this code with this error:

% Custom State Estimation
Ts=1;ts=0.1;
A=[1 0;0 1];
B=[0.0936 0.0936 0 0.0936;0 0.0752 0 0];
C=[1 0;0 1];
D=[0 0 0 0; 0 0 0 0];
plant = ss(A,B,C,D);
plant = setmpcsignals(plant,MV=[1 2 3],MD=4)
mpcobj=mpc(plant,ts,10,3)
setEstimator(mpcobj,'custom');
sys=c2d(ss(plant),Ts);
xsys=[0;0];
xmpc = mpcstate(mpcobj);
SOCpbref=75; % (en pourcentage)
SOCliref=85; % (en pourcentage)
t1=25; % en seconds
Cmaxpb=22020; % As (Ampersecond)
Cmaxli=6000; % As (Ampersecond)
Ipb=[60 65 70 75 65 60 55 50 50 50 55 60 65 70 75 75 75 75 70 60 60 55 65 60 50]; % en Ampere
Ili=[70 75 80 85 75 70 65 60 60 60 65 70 75 80 85 85 85 85 80 70 70 65 75 70 60]; % en Ampere
Cpb= sum(Ipb)/t1;
Cli= sum(Ili)/t1;
SOCpb=(Cpb/Cmaxpb);
SOCli=(Cli/Cmaxli);
for t = 0:3
    y = sys.C*xsys; % plant equations: output
    YY(t+1) = y;
    xmpc.Plant = [SOCpb, SOCli]; % state estimation
    u = mpcmove(mpcobj,xmpc,[],[SOCpbref, SOCliref]); % y is not needed
    UU(t+1) = u;
    xsys = sys.A.*xsys + sys.B.*u; % plant equations: next state
end

Unable to perform assignment because the left and right sides have a different number of elements.

Error in customstateestimation (line 28)

YY(t+1) = y;

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Answer 1

Askic V 2023-5-22

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https://ww2.mathworks.cn/matlabcentral/answers/1970209-unable-to-perform-assignment-because-the-left-and-right-sides-have-a-different-number-of-elements#answer_1241604

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Not really sure what you're trying to simulate here.

From what I can see in the code, you have created a MIMO system with 4 inputs and 2 outputs. Out of these 4 inputs, 3 inputs are manipulted variable and 4th input is measured disturbance.

When simulating systems in statespace, you shouldn't use element wise operations such as multiplication, but bnormal multiplication, since dimensions must agree.

So in addition to what @KSSV already suggested, you need to pay attention to the fact that line u = mpcmove(mpcobj,xmpc,... wil produce vector u with three elements i.e. dimension 3x1. So again, you'll have a mismatch.

One way to overcome this would be the following:

for t = 0:3
    y = sys.C*xsys; % plant equations: output
    YY(t+1,:) = y;
    xmpc.Plant = [SOCpb, SOCli]; % state estimation
    u = mpcmove(mpcobj,xmpc,[],[SOCpbref, SOCliref]); % y is not needed
    u = [u;0]; % add 4th row in order to match dimensions
    UU(t+1,:) = u;
    xsys = sys.A*xsys + sys.B*u; % plant equations: next state, no need for element-wise operation
end