# Thread: least square fit method

1. ## least square fit method

i have to least square fit function l=C/(1+e^(at))

here i have e^(at) in denominator how to bring it in terms of
Y=AX+B

2. ## Re: least square fit method

are you saying you have a data set that you expect can be modeled by $\dfrac C {1+e^{a t}}$ and you want to estimate $a$ and $C$ from a least squares fit to your data?

3. ## Re: least square fit method

YES I KNOW FOR y=e^(at) we take log on both sides and compare with linear function y=ax+b
but here e^(at) is in denominator

4. ## Re: least square fit method

Originally Posted by prasum
i have to least square fit function l=C/(1+e^(at))
here i have e^(at) in denominator how to bring it in terms of Y=AX+B
You cannot on a direct way. Use a non-linear method of regression : Nonlinear regression - Wikipedia, the free encyclopedia
Nevertheless, it can be transformed to a linear regression thanks to a method using an integral equation, paper published on Scribd : Régressions et équations intégrales
page 17 : see the computation in the case y=a+b*exp(c*x)
To apply in your case : l=C/(1+e^(A*t)) , let y=1/l ; a=b=1/C ; c=A
The publisched method requires to be slightly adaped in the particular case a=b. Contact me if you intend to try this method.