The background you requested are energetic level (joules) in a group of
starved fish over a time period of 45 days. Weekly, fish (n=5) were removed
killed and measured for energy. This was done at three temperatures. I am
comparing the rates at which the fish consume stored body energy at each of
the three temperatures. Initial data looks like the colder fish
have different rates (as would be expected) than do warmer fish. In all
cases the slope is greatest at the beginning of the curve and flattens after
several weeks. This is what is interesting - where in time the line
starts to flatten out.
By calculating a non-linear equation of a line, I was hoping to use the
first and second derivatives of the function to compare and explain
differences between the three temperature.
The data originally posted was an example of one of the curves experienced.
kc
On Thu, Aug 26, 2010 at 9:48 AM, David Winsemius <dwinsem...@comcast.net>wrote:
>
> On Aug 26, 2010, at 1:35 PM, Marlin Keith Cox wrote:
>
> I need the parameters estimated for a non-linear equation, an example of
>> the
>> data is below.
>>
>>
>> # rm(list=ls()) I really wish people would add comments to destructive
>> pieces of code.
>>
>
> Time<-c( 0, 0, 0, 0, 0, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 4, 4, 4,
>> 4, 4, 5, 5, 5, 5, 5, 8, 8, 8, 8, 8)
>> Level<-c( 100, 110, 90, 95, 87, 60, 65, 61, 55, 57, 40, 41, 50,
>> 47,
>> 44, 44, 42, 38, 40, 37, 37, 35, 40, 34, 32, 20, 22, 25, 27,
>> 29)
>> plot(Time,Level,pch=16)
>>
>
> You did not say what sort of "non-linear equation" would best suit, nor did
> you offer any background regarding the domain of study. There must be many
> ways to do this. After looking at the data, a first pass looks like this:
>
> > lm(log(Level) ~Time )
>
> Call:
> lm(formula = log(Level) ~ Time)
>
> Coefficients:
> (Intercept) Time
> 4.4294 -0.1673
>
> > exp(4.4294)
> [1] 83.88107
> > points(unique(Time), exp(4.4294 -unique(Time)*0.1673), col="red", pch=4)
>
> Maybe a Weibull model would be more appropriate.
>
>
> --
>
> David Winsemius, MD
> West Hartford, CT
>
>
--
M. Keith Cox, Ph.D.
Alaska NOAA Fisheries, National Marine Fisheries Service
Auke Bay Laboratories
17109 Pt. Lena Loop Rd.
Juneau, AK 99801
keith....@noaa.gov
marlink...@gmail.com
U.S. (907) 789-6603
[[alternative HTML version deleted]]
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
