lsqcurvefit initial values stays the same

Question

kai chung 2019-9-4

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/478835-lsqcurvefit-initial-values-stays-the-same

评论： Jasmine Boparai 2021-9-3

Hi all, I am working on this non-linear square curvefit function, however, despite many attempts, the initial guessess were always chosen despite of given boundaries. Unbounded worked. But that isn't within the bounds. I really at my end of working on possible ideas. The data given as a total of 101 for each array.

EDIT: I have made some changes which is now bounded and using the default trust-region-reflective algorithm

T = readtable('skin3.csv','ReadVariableNames',true); %skin3 Measured data
x = T{:,1}; %freq
y = T{:,2}; %real
%Transpose
freq = x.';
e_real = y.';
%optimoptions(@lsqnonlin,'StepTolerance',1e-6);
options = optimset('MaxFunEvals',10000);
options=optimset(options,'MaxIter',10000);
guess = 40;
UB = guess + 10;
LB = guess - 10;
lb = [-20,LB,1,0,-0.1];
ub = [20,UB,40,1,0.1];
x0 = [0.9,guess,8.2,0.236,0.05];
x  = lsqcurvefit(@flsq,x0,freq,e_real,lb,ub,options)
e_f = x(1);
e_del = x(2)*1e2;
tau1 = x(3)*1e-12;
alf1 = x(4);
sig = x(5);
yfit = real(flsq(x,freq));
%plot e_real against freq
plot(freq,e_real,'k.',freq,yfit,'b-')
legend('Data','Fitted exponential')
title('Data and Fitted Curve')

Function:

function y = flsq(x,freq)
    x(3)=x(3)*1e-12;
    y = x(1) + (x(2)-x(1))./(1 + ((1j*2*pi.*freq*x(3)).^(1-x(4))))+x(5)./(1j*2*pi*freq*8.854e-12);
    
end

As you can see the result remained the same while the curve is not even close: