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solving complex matrix with symbolic variables

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ZENONG
ZENONG 2023-6-22
回答： Torsten 2023-6-22
hello, I am trying to solve a complex matrix with symbols, but it returns''Empty sym: 0-by-1''. I would like to know why this happened and how could I solve this problem. Thank you.
  1 个评论
ZENONG
ZENONG 2023-6-22
Hi, I updated my code, and it retured values, but I believe there still are some errors, maybe the ''theta'' and ''abs'' variables?

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Vishnu
Vishnu 2023-6-22
Hi Zenong,
From the code, it seems that you are trying to solve the complex matrix equations using symbolic variables.However, the issue is that the variables used for 'VI' and 'Vscl' are not symbolic variables, and this is causing the error "Empty sym: 0-by-1".
To solve this issue, the you need to define symbolic variables 'p1', 'q1', 'p2', 'q2', 'p3', 'q3', 'p4' and 'q4' using 'syms' function.
syms a b c d e f g h k p1 p2 p3 p4 q1 q2 q3 q4
Here is the modified code:
syms a b c d e f g h k real %defining symbolic variables
z1=-30j;
z2=0.08+0.40j;
z3=-35j;
z4=0.10+0.50j;
z5=0.10+0.50j;
z6=-25j;
z7=0.30j;
p1=a;
p2=0.55;
p3=0.30;
p4=0.50;
q1=1j*b;
q2=0.15j;
q3=0.201j;
q4=1j*c;
e1=1.05;
e2=d;
e3=e;
e4=f;
f1=0j;
f2=1j*g;
f3=1j*h;
f4=1j*k;
y11=1/z1+1/z2+1/z5;
y12=(-1)*1/z2;
y13=(-1)*1/z5;
y14=0;
y21=y12;
y22=1/z2+1/z4+1/z3;
y23=(-1)*1/z4;
y24=0;
y31=y13;
y32=y23;
y33=1/z6+1/z7+1/z5+1/z4;
y34=0;
y41=y14;
y42=y24;
y43=y34;
y44=1/z7;
Y=[y11,y12,y13,y14;
y21,y22,y23,y24;
y31,y32,y33,y34;
y41,y42,y43,y44];
conjY=conj(Y); %conjugate Y
V=[e1+f1;e2+f2;e3+f3;e4+f4];
format shortG
conjY=round(conjY,2,'significant') %conjugate Y
Vscl=diag(V) %scalar matrix V
conjV=conj(V) %conjugate V
%Defining symbolic variables
syms a b c d e f g h k p1 p2 p3 p4 q1 q2 q3 q4
[a,b,c,d,e,f,g,h,k] = solve([p1+q1;p2+q2;p3+q3;p4+q4]==Vscl*conjY*conjV,[a,b,c,d,e,f,g,h,k]);

更多回答（2 个）

MANIK
MANIK 2023-6-22
编辑：MANIK 2023-6-22
Hi @ZENONG,
As per my understanding, you're trying to solve a complex matrix equation in MATLAB
Well, I was going through your code, it is all correct. But, here you're trying to solve a problem, which contains 4 equations and 9 variables which is not possible. That's why you're getting an error here.
Torsten
Torsten 2023-6-22
Ran in:
syms a b c d e f g h k real
z1=-30j;
z2=0.08+0.40j;
z3=-35j;
z4=0.10+0.50j;
z5=0.10+0.50j;
z6=-25j;
z7=0.30j;
p1=a;
p2=-0.55;
p3=-0.30;
p4=0.50;
q1=1j*b;
q2=-0.15j;
q3=-0.20j;
q4=1j*c;
e1=1.05;
e2=d;
e3=e;
e4=f;
f1=0j;
f2=1j*g;
f3=1j*h;
f4=1j*k;
y11=1/z1+1/z2+1/z5;
y12=(-1)*1/z2;
y13=(-1)*1/z5;
y14=0;
y21=y12;
y22=1/z2+1/z4+1/z3;
y23=(-1)*1/z4;
y24=0;
y31=y13;
y32=y23;
y33=1/z6+1/z7+1/z5+1/z4;
y34=(-1)*1/z7;
y41=y14;
y42=y24;
y43=y34;
y44=1/z7;
theta=f^2+k^2;
abs=1.1^2;
Y=[y11,y12,y13,y14;
y21,y22,y23,y24;
y31,y32,y33,y34;
y41,y42,y43,y44];
conjY=conj(Y);
V=[e1+f1;e2+f2;e3+f3;e4+f4];
format shortG
conjY=round(conjY,2,'significant');
Vscl=diag(V);
conjV=conj(V);
VIt=Vscl*conjY*conjV;
P=simplify([real([p1;p2;p3;p4]);imag([q1;q2;q3;q4]);theta])
P = 
Q=simplify([real(VIt);imag(VIt);abs])
Q = 
sol=vpasolve(P==Q)
sol = struct with fields:
a: [4×1 sym] b: [4×1 sym] c: [4×1 sym] d: [4×1 sym] e: [4×1 sym] f: [4×1 sym] g: [4×1 sym] h: [4×1 sym] k: [4×1 sym]
sol.a
ans = 
sol.b
ans = 
sol.c
ans = 
sol.d
ans = 
sol.e
ans = 
sol.f
ans = 
sol.g
ans = 
sol.h
ans = 
sol.k
ans = 
error = arrayfun(@(i)subs(P-Q,[a b c d e f g h k],[sol.a(i) sol.b(i) sol.c(i) sol.d(i) sol.e(i) sol.f(i) sol.g(i) sol.h(i) sol.k(i)]),1:4,'UniformOutput',0)
error = 1×4 cell array
{9×1 sym} {9×1 sym} {9×1 sym} {9×1 sym}
error{1}
ans = 
error{2}
ans = 
error{3}
ans = 
error{4}
ans = 

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