How to change parameters in exp2 fit???
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Hello, Sorry for the question, im just a very beginner. I am using f=fit(Wavelength_sal_cor(517:1293),Salinity_and_Particle_corrected_spectra(517:1293),'exp2');
It calculate all 4 coefficients, but sometimes I have negative values, then fit is not good, I want to set parameters of second exp as constants 'c' as meaning(at defined x): Salinity_and_Particle_corrected_spectra(998), and d as -0.01. But I don´t understand how to do.
Could you help me please?
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Antworten (2)
Shashank Prasanna
am 28 Jul. 2013
You can specify a custom model with your requirements instead of using the exp2
model = @(z)z(1)*exp(z(2)*x)+Salinity_and_Particle_corrected_spectra(998)*exp(-0.01*x)
% Where c = Salinity_and_Particle_corrected_spectra(998) and
% d = -0.01
f=fit(Wavelength_sal_cor(517:1293),Salinity_and_Particle_corrected_spectra(517:1293),model);
You could also specify 'StartPoint','Lower' and 'Upper' bounds to get better results.
There are examples in the documentation on how to fit custom models:
2 Kommentare
Shashank Prasanna
am 28 Jul. 2013
Bearbeitet: Shashank Prasanna
am 28 Jul. 2013
Lets forget about your code for a moment. Are you able to run the example in the documentation link I provided without any errors?
If that is working fine then we may need more info about your code.
If the documentation example also shows the same error, you may have a path issue. Try restoredefaultpath
Jon Cherrie
am 21 Aug. 2013
I think that the anonymous function, model, is not set up correctly for use by Curve Fitting Toolbox. Try this instead:
c = Salinity_and_Particle_corrected_spectra(998);
d = -0.01;
model = @(a, b, x) a*exp( b*x ) + c*exp( d*x );
f = fit( Wavelength_sal_cor(517:1293), Salinity_and_Particle_corrected_spectra(517:1293), model );
To get good results, you will probably need to supply an estimate of the start point, StartPoint.
Alexandra
am 28 Jul. 2013
1 Kommentar
Shashank Prasanna
am 28 Jul. 2013
What you posted here is not an answer to your questions but rather a comment to my answer. Please see my reply on the comment to my answer.
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