How to enter a sigmoidal equation for a curve fit with lsqfitting

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he tratado de ingresar esta ecuación sigmoidal para un ajunste de curva lsqcurvefit con esta ecuación
y=1/(1+exp(4a(b-X)+2))
fun=@(x,xdata)1./(1+exp(4.*x(1).*(x(2) - xdata)+2))
x=lsqcurvefit(fun,x0,xdata,ydata)
he podido leer los datos aunque no he podido hacer los ajustes, al parecer reconoce al exponecial pero no los ajuste con X(1) y x(2).
alquien me podra ayudar con este tema
  3 Kommentare
Matt J
Matt J am 10 Dez. 2023
You haven't provided the data we would need to run the code. Most likely, though, the problem is your x0 has been chosen randomly (and therefore, poorly).
Wilfredo
Wilfredo am 10 Dez. 2023
Gracias Matt J, x0= [0 5900] puede ser que aqui este el error entonces.

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Image Analyst
Image Analyst am 9 Dez. 2023
See my attached demo where I fit data to the rate equation (a sigmoid type of formula).
Adapt as needed, like using a different sigmoid formula. If you have problems, write back and attach your data and m-file.
  8 Kommentare
Wilfredo
Wilfredo am 11 Dez. 2023
Hello friend, thank you very much for your help, it helps me a lot, for the values I expect are for A=0.000186865 and B=3524.
Wilfredo
Wilfredo am 11 Dez. 2023
throws up the following error.
Warning: The Jacobian at the solution is ill-conditioned, and some model parameters may not be estimated well (they are not
identifiable). Use caution in making predictions.

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