Help with a fit

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aurc89 2014-3-21

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评论： aurc89 2014-3-21

Hello! I have a set of data (x,y) which describes a function y=f(x). I would like to fit this function with a biexponential function made like this : f(x) = a*exp(-x/b)+c*exp(-x/d)+e and retrieve the values of a,b,c,d,e. Can you help me to do this? Thank you!

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Mischa Kim 2014-3-21

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编辑：Mischa Kim 2014-3-21

在 MATLAB Online 中打开

Aurc89, does this help?

 a = 1; b = 1; c = 1; d = 1; e = 1;
 x = (0:0.1:2)';
 y = a*exp(-x/b)+c*exp(-x/d)+e + 0.1*rand(length(x),1);
 f = fit(x,y,'exp2');
 plot(f,x,y)

The fitting coefficients are accessed, e.g., via

f.a

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Mischa Kim 2014-3-21

编辑：Mischa Kim 2014-3-21

Aurc89: You're welcome.

John: I was not trying to generate random noise, thanks for the polite pointer, though.

aurc89 2014-3-21

Sorry, the last question: this kind of command gives me the fit with the function f(x) = a*exp(b*x) + c*exp(d*x). Instead, I woud like to have a fit with this kind of function: f(x) = a*exp(b*x) + c*exp(d*x) + g. I need the constant term g also, because the time constants of the biexponential changes with g (because I am differently close to zero axis by changing 'g', so b and d are different). Is there an authomatic way to do this? Thank you very much in advance

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