Thank you. Could you lastly help me with this error.  I was trying to use a
self starting function (Weibull).

model<-nls(Level~ SSweibull(Time,Asym,Drop,lrc,pwr))

Error in qr.default(.swts * attr(rhs, "gradient")) :
NA/NaN/Inf in foreign function call (arg 1)



On Thu, Aug 26, 2010 at 1:42 PM, David Winsemius <dwinsemius@comcast.net>wrote:

>
>  On Aug 26, 2010, at 5:20 PM, Marlin Keith Cox wrote:
>
>  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.
>
>
> You might be interest in what happens when you expand the plot a bit using
> the fm1 model:
>
>  plot(Level~Time, xlim=c(0,40), ylim=c(0,max(Level))  )
>  lines(0:40, predict(fm1, data.frame(Time=0:40 ) ) , col="red", pch=4)
>  abline(h=0)
>
> And not forgetting that extrapolation beyond the limits of data is a
> dangerous maneuver. In this instance any Weibull model would predict some
> sort of decay to 0, which may or may not be scientifically plausible.
>
> --
> David.
>
>
> kc
>
> On Thu, Aug 26, 2010 at 9:48 AM, David Winsemius <dwinsemius@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.Cox@noaa.gov
> marlinkcox@gmail.com
> U.S. (907) 789-6603
>
>
>   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.Cox@noaa.gov
marlinkcox@gmail.com
U.S. (907) 789-6603

	[[alternative HTML version deleted]]

