Info

# Error : Matrix dimensions must agree

2 views (last 30 days)
Ahmad Sheikh on 24 Oct 2015
Closed: MATLAB Answer Bot on 20 Aug 2021
I have written the follwing LMI in matlab
(A1-B*F1)' * P * (A1-B*F1) - P < 0
where, A1 is a 12 x 12 matrix B is a 12 x 4 matrix and F1 is a 4 x 12 matrix
A1=[0 0 0 0 0 0 1 0 0 0 0 0;0 0 0 0 0 0 0 1 0 0 0 0;0 0 0 0 0 0 0 0 1 0 0 0;0 0 0 0 0 0 0 0 0 0 0 1;0 0 0 0 0 0 0 0 0 0 1 0;0 0 0 0 0 0 0 0 0 1 0 0;0 0 0 0 -9.4757 2.539 0 0 0 0 0 0;0 0 0 0 2.539 9.4757 0 0 0 0 0 0;0 0 0 0 0 0 0 0 0 0 0 0;0 0 0 0 0 0 0 0 0 0 0 0;0 0 0 0 0 0 0 0 0 0 0 0;0 0 0 0 0 0 0 0 0 0 0 0];
B=[0 0 0 0;0 0 0 0;0 0 0 0;0 0 0 0;0 0 0 0;0 0 0 0;0 0 0 0;0 0 0 0;-1.4286 0 0 0;0 0.24162 0 0;0 0 0.24162 0;0 0 0 0.80541];
setlmis([]);
P=lmivar(1,[12 1]);
F1=lmivar(2,[4 12]);
lmiterm([1 1 1 P],(A1-B*F1)',(A1-B*F1));
lmiterm([1 1 1 P],1,-1);lmis=getlmis;
[tmin,xfeas]=feasp(lmis);
f1=dec2mat(lmis,xfeas,F1)
but its giving an error '' Matrix dimensions must agree '' can some one help why?

dpb on 24 Oct 2015
(A1-B*F1)' * P * (A1-B*F1) - P < 0
where, A1 is a 12 x 12 matrix B is a 12 x 4 matrix and F1 is a 4 x 12 matrix
(A1-B*F1)' * P * (A1-B*F1)
[12x12] * [12 1] --> [12x1] * [12x12]
BOOM! You're trying to multiply a column vector on the left of the square array...
Ahmad Sheikh on 24 Oct 2015
Edited: Ahmad Sheikh on 24 Oct 2015
well
P=lmivar (1,[12 1])
it doesnt show that P is a 12x1 matrix.
dpb on 24 Oct 2015
Oh, yeah? Syntax surely looks like it would be....so what is it?
But whatever, work thru the expression as shown; bound to find somewhere it breaks down -- maybe there's a problem in association/precedence in computer evaluation from what is intended mathematically?