Add constants in nlinfit

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Silke 2017-12-21

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https://ww2.mathworks.cn/matlabcentral/answers/374096-add-constants-in-nlinfit

评论： Star Strider 2017-12-22

采纳的回答： Star Strider

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Hi there,

is there a way that I provide nlinfit with some constants that are taken into account when solving a function?

So, for example, I use this code for nlinfit:

[xfit,resnorm, Jacob, CovB, MSE] = nlinfit(  handles.timecorr,handles.datacorr',@DiffEqSolver300, B );

I would like to give another set of parameters to the function DiffEqSolver300 that should not be fitted, but they depend on calculations that happens before I call the nlinfit function. Is this somehow possible?

Just a simple example. Let's assume the function that should be fitted is

y = A*x + B;

Depending on some input parameters, A could be 1 or 10 or 100 and B is a fitting parameter. How can I tell the function which value A should have?

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Answer 1

Star Strider 2017-12-21

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https://ww2.mathworks.cn/matlabcentral/answers/374096-add-constants-in-nlinfit#answer_297338

编辑：Star Strider 2017-12-21

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Writing your own objective function, you simply need to pass ‘A’ as a parameter.

Example —

objfcn = @(B,x,A) A*x + B;

then call it in nlinfit as:

beta = nlinfit(x, y, @(B,x) objfcn(B,x,A), ... );

so that ‘objfcn’ accepts ‘A’ as a parameter, and the function works with nlinfit as it would if no additional parameters were passed.

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Silke 2017-12-22

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I am still confused about how this works. Well, I think it is not really necessary to understand what DiffEqSolver300 does, as it is quite a general problem. I have now defined the function like this

function dCCconv = DiffEqSolver300(param, t, FA, WL);

and I am using nlinfit like this:

[xfit,resnorm, Jacob, CovB, MSE] = nlinfit(  handles.timecorr,handles.datacorr',@(param,t) DiffEqSolver300(param, t, FA, WL), handles.x0 );

I am not sure if this is the correct way to do it, as for example "param" is not defined in the matlab script that uses nlinfit. But handles.x0 is giving the "param" to DiffEqSolver300.

However, I tried it like that, and I got the following error message: Error using nlinfit (line 205) Error evaluating model function '@(param,t)DiffEqSolver300(param,t,FA,WL)'.

Error in TRMC_GuiFit_SD_DiffEqfit_1>FITANDPLOT_Callback (line 416) [xfit,resnorm, Jacob, CovB, MSE] = nlinfit( handles.timecorr,handles.datacorr',@(param,t) DiffEqSolver300(param, t, FA, WL), handles.x0 );%, handles.lb, handles.ub

Error in gui_mainfcn (line 95) feval(varargin{:});

Error in TRMC_GuiFit_SD_DiffEqfit_1 (line 42) gui_mainfcn(gui_State, varargin{:});

Error in matlab.graphics.internal.figfile.FigFile/read>@(hObject,eventdata)TRMC_GuiFit_SD_DiffEqfit_1('FITANDPLOT_Callback',hObject,eventdata,guidata(hObject))

Caused by: Not enough input arguments.

Error while evaluating UIControl Callback

What am I doing wrong here?

Silke 2017-12-22

Thanks for your help. Indeed, it is working now. I had an error in DiffEqSolver300.

Star Strider 2017-12-22

As always, my pleasure.

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Add constants in nlinfit

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