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我正在尝试在下面的代码中评估 G11 symfun，但它失败并继续向我显示我选择按照代码中指定的方式设置的变量 t，我什至尝试使用“subs”命令，但它也失败了。我定义了必要的符号和变量，但 t 变量并没有在 'G11' symfun 中评估，还有另一个类似的 symfun，例如 G12 或 K12，但在它们中评估的 t 变量是我的代码

% Defining the variables as symbols.
clear all, close all 
clc
syms x xi q_1 q_2 q_3 q_4 q_01 q_02 q_03 q_04 EI Mr M m L t Omega S1 S2 S3 
...
S4 S5 S6 S7 S8 w L_dot U U_dot g L_ddot M11 M22
% Defining the general coordinates and the trial function.
L_ddot=0;
g=9.8;
Mr=M/(M+m);
PHI(x,t)=[sqrt(2).* sin(pi.*(xi)) sqrt(2).* sin(2*pi.*(xi)) sqrt(2).* 
sin(3.*pi.*(xi)) sqrt(2).* sin(4.*pi.*(xi))];
q_1(t)= S1*exp(sqrt(-1)*w*t);  
q_01(t)= S5*exp(sqrt(-1)*w*t);
q_2(t)= S2*exp(sqrt(-1)*w*t); 
q_02(t)= S6*exp(sqrt(-1)*w*t);
q_3(t)= S3*exp(sqrt(-1)*w*t); 
q_03(t)= S7*exp(sqrt(-1)*w*t);
q_4(t)= S4*exp(sqrt(-1)*w*t); 
q_04(t)= S8*exp(sqrt(-1)*w*t);
Q_v(t) =[q_1;q_2;q_3;q_4];
Q_w(t) =[q_01;q_02;q_03;q_04];
V(x,t) = PHI*Q_v(t);
W(x,t) = PHI*Q_w(t);
% Defining the coeficients of the ODE.
U(x,t)=U;
L(x,t)=1+0.1*t;
L_dot(x,t)=diff(L,'t',1);
L_ddot=0;
M11=int(PHI'*PHI,'xi',[0 1]);
M22=M11;
G11=(2*(L_dot/L))* int((2-xi)*PHI'*diff(PHI,'xi',1),'xi',[0 1])+2*Mr* 
(U/L)*int(PHI'*diff(PHI,'xi',1),'xi',[0 1]);
G12=-2*Omega*int(PHI'*PHI,'xi',[0 1]);
G21=-G12;
G22=G11;
K11=(EI/((M+m)*L^4))*int(PHI'*diff(PHI,'xi',4),'xi',[0 1])+ (L_dot/L)^2 
*int((2-xi)^2 *...
PHI'*diff(PHI,'xi',2),'xi',[0 1])+ ((L_ddot*L-2*L_dot^2)/L^2)*int((1- 
xi)*PHI'*diff(PHI,'xi',1),'xi',[0 1]) ...
+ 2*Mr*(L_dot*U/L^2)*int((2-xi)*PHI'*diff(PHI,'xi',2),'xi',[0 1])+ Mr* 
(U/L)^2 *int(PHI'*diff(PHI,'xi',2),'xi',[0 1])-...
(g-((L_ddot-2*L_dot^2)/L))*int((1-xi)*PHI'*diff(PHI,'xi',2),'xi',[0 1])+ 
(g/L)*int(PHI'*diff(PHI,'xi',1),'xi',[0 1])-...
Omega^2 * int(PHI'*PHI,'xi',[0 1]);

K12= -2*Omega*(L_dot/L)*int((2-xi)*PHI'*diff(PHI,'xi',1),'xi',[0 1])-2*Mr* 
((U*Omega)/L)*int(PHI'*diff(PHI,'xi',1),'xi',[0 1]);
K21=-K12;
K22=K11;
% evaluating the Coefficient matrices for the time history 1 to 80 seconds 
by the stepping of 0.1 .
t=0:0.1:80;
m=8;
M=2;
Mr=0.2;
x=1;
U=2; % the flow velocity
Omega=90;
EI=8.9782;
FUNM11 = matlabFunction(M11);  
Mmatrix11 = feval(FUNM11); 
FUNG11 = matlabFunction(G11);  
Gmatrix11 = feval(FUNG11,t,U,Mr,L_dot,L);
FUNG12 = matlabFunction(G12);  
Gmatrix12 = feval(FUNG12, t,x,Omega);  
FUNK11 = matlabFunction(K11);  
Kmatrix11 = feval(FUNK11, t,M,x,Omega,m,U,EI);
FUNK12 = matlabFunction(K12);  
Kmatrix12 = feval(FUNK12, t,M,x,U,m,Omega); 
Mmatrix22=Mmatrix11;
Gmatrix21=-Gmatrix12;
Gmatrix22=Gmatrix11;
Kmatrix21=-Kmatrix12;
Kmatrix22=Kmatrix11;
% Assembling the Coeficient matrices
Q=[Q_v;Q_w];
Mmatrix=[Mmatrix11 ,zeros(size(Mmatrix11)); zeros(size(Mmatrix11)) 
Mmatrix22];
Gmatrix=[Gmatrix11 Gmatrix12; Gmatrix21 Gmatrix22];
Kmatrix=[Kmatrix11 Kmatrix12; Kmatrix21 Kmatrix22];

在组装我的系数矩阵后，我尝试为 w 求解这个代数方程：

  eqn=det(-w^2.*Mmatrix+i*w.*Gmatrix+Kmatrix)==0;

其中 w 是系统的频率。

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