nlinfit gives no result

Question

Silke 2017-11-8

0
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https://ww2.mathworks.cn/matlabcentral/answers/365865-nlinfit-gives-no-result

回答： Eric 2017-11-9

采纳的回答： Eric

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Hello!

When trying to fit data with nlinfit, I get the following error message:

Warning: Rank deficient, rank = 0, tol = 0.000000e+00. > In nlinfit>LMfit (line 574) In nlinfit (line 276) In TRMC_GuiFit_v2_tmax_SD_nlfit>FITANDPLOT_Callback (line 491) In gui_mainfcn (line 95) In TRMC_GuiFit_v2_tmax_SD_nlfit (line 42) In matlab.graphics.internal.figfile.FigFile/read>@(hObject,eventdata)TRMC_GuiFit_v2_tmax_SD_nlfit('FITANDPLOT_Callback',hObject,eventdata,guidata(hObject)) Warning: Some columns of the Jacobian are effectively zero at the solution, indicating that the model is insensitive to some of its parameters. That may be because those parameters are not present in the model, or otherwise do not affect the predicted values. It may also be due to numerical underflow in the model function, which can sometimes be avoided by choosing better initial parameter values, or by rescaling or recentering. Parameter estimates may be unreliable. > In nlinfit (line 373) In TRMC_GuiFit_v2_tmax_SD_nlfit>FITANDPLOT_Callback (line 491) In gui_mainfcn (line 95) In TRMC_GuiFit_v2_tmax_SD_nlfit (line 42) In matlab.graphics.internal.figfile.FigFile/read>@(hObject,eventdata)TRMC_GuiFit_v2_tmax_SD_nlfit('FITANDPLOT_Callback',hObject,eventdata,guidata(hObject)) Warning: Matrix is close to singular or badly scaled. Results may be inaccurate. RCOND = 1.999277e-56. > In nlparci (line 104) In TRMC_GuiFit_v2_tmax_SD_nlfit>FITANDPLOT_Callback (line 492) In gui_mainfcn (line 95) In TRMC_GuiFit_v2_tmax_SD_nlfit (line 42) In matlab.graphics.internal.figfile.FigFile/read>@(hObject,eventdata)TRMC_GuiFit_v2_tmax_SD_nlfit('FITANDPLOT_Callback',hObject,eventdata,guidata(hObject)) Warning: Imaginary parts of complex X and/or Y arguments ignored > In TRMC_GuiFit_v2_tmax_SD_nlfit>FITANDPLOT_Callback (line 657) In gui_mainfcn (line 95) In TRMC_GuiFit_v2_tmax_SD_nlfit (line 42) In matlab.graphics.internal.figfile.FigFile/read>@(hObject,eventdata)TRMC_GuiFit_v2_tmax_SD_nlfit('FITANDPLOT_Callback',hObject,eventdata,guidata(hObject)) >>

Posting the code is a bit tricky, but I will do my best.

      [xfit,resnorm, Jacob, CovB, MSE] = nlinfit(  handles.timecorrcrop,handles.datacorrcrop',@funexp2conv410, handles.x0 ); 
handles.timecorrcrop = -1e-7:250e-12:1e-6;
handles.a1_GUESS_VALUE = 0.6;
handles.G1_GUESS_VALUE = 2.5e-8;
handles.a2_GUESS_VALUE = 0.4;
handles.G2_GUESS_VALUE = 3.5e-7;
handles.ETAMU_0_GUESS_VALUE = 0.04; 
handles.x0 = [ handles.a1_GUESS_VALUE; 1/handles.G1_GUESS_VALUE; handles.a2_GUESS_VALUE; 1/handles.G2_GUESS_VALUE; handles.ETAMU_0_GUESS_VALUE ];

With the function being:

   function f = funexp2conv410( param, t )
      RC = 18e-9; % Time constant of cavity cell
      a1 = param(1); % Parameters for bi-exponential decay
      D1 = param(2);
      a2 = param(3);
      D2 = param(4);
      etamu1 = param(5); %starting value of conductivity in cm2/Vs
      assignin('base', 'D1', D1);
      assignin('base', 'D2', D2);
       filename1 = 'pulse410.txt';
       pathname1 = 'D:\PulseShapes\';
       pulse410 = importfile1([pathname1, filename1]);
      [P,I] = max(pulse410(:,1)); %find the coordinates of the maximum value of t
       t_in = find(t==P); 
       t_x = t(1:t_in); 
       pulse410s=spline(pulse410(:,1), pulse410(:,2), t_x); % make the pulse and the experimental data have the same time scale
      f1x = conv(a1 * exp(-t*D1) + a2 * exp(-t*D2), pulse410s./75.5856) 
      f1(1:4000) = etamu1*f1x(1:4000);
      assignin('base','f1',f1);
      f2x = conv(exp(-t/RC),f1);
      f(1:4000) = f2x(1:4000)/72.501;