[R] Need to replicate Boltzman Signmodial Curve fit from Graph Pad

[peter dalgaard]

On Apr 23, 2013, at 18:45 , R. Michael Weylandt wrote:

> On Tue, Apr 23, 2013 at 3:55 PM, J J <rnoobier at gmail.com> wrote:
>> Hello useRs (please don't kill me),
>> 
>> I've fairly new to R having only a few months of playing around with R.
>> What little I've learned has been extremely useful.
>> 
>> If someone could point me as to how to replicate the Boltzman Sigmodial
>> curve fit as provided by Graphpad software I'd be eternally grateful.
>> 
>> Where  we currently use Graphpad for only this one function,its seems
>> highly inefficient for a $100 piece of software to be used for only one
>> function (which isn't nearly as bad as the company's pandemic reliance on
>> Excel for nearly everything else).
>> 
>> so anyway, what I'd normally do is take a set of data like this:
>> 
>> pH counts  3.8 968  5.0 1347  5.8 2867  6.6 9203  7.0 15817  7.4 20297  8.2
>> 31916  9.2 35756
>> then fit this to a Boltzman sigmodial in Graphpad. Graphpad spits out a
>> much longer set of vectors and also information about v50 and confidence
>> intervals etc (if anyone is familiar with that software). This is what i'd
>> like to replicate.
>> 
>> It might be that I just don't know what i'm doing,so feel free to call me
>> an idiot but any help is greatly appreciated!
> 
> Being unfamiliar with the problem domain, I'd imagine that nls() would
> probably be what you're looking for. Does
> 
> ? nls
> 
> seem promising? If so, we can help you get started.

In particular, SSfpl looks tantalizingly similar to the Bolzmann sigmoidal (sic!) curve. 

-- 
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com