[R] exponential day

[Bert Gunter]

Please note that R^2 for nonlinear models is nonsense.

Search on "R^2 in nonlinear models" for details, e.g.

http://statisticsbyjim.com/regression/r-squared-invalid-nonlinear-regression/

Cheers,
Bert


Bert Gunter

"The trouble with having an open mind is that people keep coming along and
sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )


On Wed, Aug 15, 2018 at 10:54 AM Francis Boateng <
francis.boateng using versantphysics.com> wrote:

> Thanks Ellison, I will try it.
>
> Francis
>
>
> -----Original Message-----
> From: S Ellison <S.Ellison using LGCGroup.com>
> Sent: Thursday, August 9, 2018 8:12 AM
> To: Francis Boateng <francis.boateng using versantphysics.com>;
> r-help using r-project.org
> Subject: RE: exponential day
>
> > Please, how can I determine parameters from exponential equation
> > Example
> > one:  y = a*exp(-b*x);  how do I determine  a  and  b , as well as
> > R-square from data sets. And also fitting y = a*exp(-b*x) into the
> > data sets Assuming data sets A = (0,2,4,6,8,10) B =
> > (1,0.8,0.6,0.4,0.2,0.1)
>
> For least squares fitting, you could take logs and do a simple linear fit,
> if the resduals are reasonably homoscedastic in the log domain (or if you
> can sort the weighting out properly).
>
> For non-linear least squares, look at ?nlm, ?nls or (if you want to roll
> your own) ?optim
>
> For max likelihood, maybe nlme in the nlme package.
>
> For other ideas, look up 'non-linear fitting with R' on any search engine,
> or check the R Task Views
>
> S Ellison
>
>
>
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