Simple lsqcurvefit does not work properly

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Henrik Schädlich 2017-10-30

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https://ww2.mathworks.cn/matlabcentral/answers/364131-simple-lsqcurvefit-does-not-work-properly

回答： Henrik Schädlich 2017-11-1

stifness.xls

Hello. I would like to do a simple lsqcurvefit. But it seems to be that I cannot write the code properly. The data is attached. For some background.

My code is:

n = 400;                        % number of partitions           
l = 13;                         % length of Basilarmembran in cm
x = linspace(0.01, 13, n)';     % length of each partition 0.01 - 13 cm
b = 0.5;                        % width in cm at Helicotrema
t = 0.04;                       % height in cm
beff = b.*x/l;                  % length of each trapezium
dx = x(2:n) - x(1:n-1);         % length of each mass oszillator 
zs = dx.*(beff(1:n-1)+2.*beff(2:n))./(3*beff(1:n-1)+3.*beff(2:n));      % centroid of an trapezial-area
xeff = zs + x(1:n-1);           % effectiv distance of each centroid 
%      ________BASIS     The tip counts from x = 0.01 cm (basis) to x = 13 cm (apex)
%     |        .        
%     |       /|\       
%    h|      /_|_\
%     |     /__|__\  <-- This is one trapezium
%     |    /   |   \    
%     |___/____|____\   
%         |_________|   APEX
filename = 'stifness.xls';
A = xlsread(filename);
xdata=A(:,1)/10;         % x-values in cm
fdata=A(:,2);            % y-values in Hz
s0 = [90, 1.7, 0.88];        % inital values, processed by hand
ub = [2e2, 2e0, 1e1];        % upper bound
lb = [1e1, 1e0, 1e-1];       % lower bound
options = optimset('TolFun',1.0e-15,'TolX',1.0e-15); 
Gfun = @(s,x)  s0(1).*(10.^(s0(2).*(13-x)/13)-s0(3));
fitfun = lsqcurvefit(Gfun,s0,xdata,fdata,lb,ub,options);
Gfuntest1 = s0(1).*(10.^(s0(2).*(13-xeff)/13)-s0(3));               % plot with inital values
Gfuntest2 = fitfun(1).*(10.^(fitfun(2).*(13-xeff)/13)-fitfun(3));   % plot with fitted values
semilogy(xeff, Gfuntest1,'g',xeff,Gfuntest2,'--k',xdata,fdata,'ob'); % plot data

Any suggestion for my little problem? I don't know, why the lsqcurvefit does not change the inital values. They are staying the same. It cannot be that I guessed perfect initial values.

Best regards

Henrik

EDIT: Sorry for the missed data. Now it is attached.

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Henrik Schädlich 2017-10-30

编辑：Henrik Schädlich 2017-10-30

I thought the lsqcurvefit should work this time. That is why I did not try the other fitting procedure.

The data is attached properly now. Hopefully it is operating sufficiently now.

Henrik Schädlich 2017-10-30

编辑：Henrik Schädlich 2017-10-30

在 MATLAB Online 中打开

Is it correct if I add:

Gfun = @(s,x)  s(1).*(10.^(s(2).*(13-x)/13)-s(3));
fitfun = @(s) norm(fdata- Gfun (s,xdata));
options = optimoptions('ga', 'InitialPopulationMatrix',s0, 'MaxGenerations', 1E+5, 'FunctionTolerance',1E-8);
[a, fval, exitflag] = ga(fitfun, 3, [], [], [], [], [], [], [], options);

Is it ok to have seven times []?

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