[求助] 使用双自由度的随机减量技术（2DOF-RD）法拟合混叠的模态信号时拟合不良的问题

%已知时间向量t1与带频率相近的混叠模态的衰减信号y
guess = [1,0.01,0.01,1,0.01,0.01,0];%未知参数的初值
guess_f = [0.1663,0.1862];%已知的两模态的频率Hz
myFun = @(a,x) a(1)./sqrt(1-a(2)^2).*exp(-a(2).*guess_f(1).*x).*cos(sqrt(1-a(2)^2).*guess_f(1).*x-a(3))+a(4)./sqrt(1-a(5)^2)*exp(-a(5).*guess_f(2).*x).*cos(sqrt(1-a(5)^2).*guess_f(2).*x-a(6))+a(7);
[coeff,R1,J1,CovB1,MSE1] = nlinfit(t1,y,myFun,guess);%t1为时间向量，y为带频率相近的混叠模态的衰减信号

%已知时间向量t1与带频率相近的混叠模态的衰减信号y
envelop = abs(hilbert(y));
envelop(1)=y(1);
guess = [1,0.01,1,0.01,0];%未知参数的初值
guess_f = [0.1663,0.1862];%已知的两模态的频率Hz
myFun = @(a,x) a(1).*exp(-a(2).*x)+a(3).*exp(-a(4).*x)+a(5);%a(1)、a(3)表示幅值，a(2)、a(4)表示阻尼与频率的乘积
[coeff,R1,J1,CovB1,MSE1] = nlinfit(t1,envelop,myFun,guess);%t表示自变量，y 表示因变量，myfun给定的含有未知参数的函数结构，guess未知参数的初值
zeta1 = abs(coeff(2)./guess_f(1));
zeta2 = abs(coeff(4)./guess_f(2));