Subject: Sum: nonlinear regressions

From: "govindan subramanian" <[email-masked]>
Date: Fri, 28 Apr 2000 05:54:36 PDT

Dear CCl'ers,
A few wanted me to summarize the replies to the CCL list.  Here it comes, 
and thanks to the five people who took time to respond.

1.  Ryszard Czerminski
http://www.informatik.uni-stuttgart.de/ipvr/bv/projekte/snns/snns.html

2.  Dr. Jerry Hintze
I recommend NCSS as a general-purpose statistics package that has an 
excellent non-linear regression routine.  However, it is not free!  I do not 
not recommend freeware in this case.  Most statistics programs are ill 
suited for the complete analysis of laboratory data.  If you want reliable 
results and a full set of statistical tests to evaluate the results, you 
want a program written by a professional statistician.  Our statisticians 
highly recommend NCSS.
It works and unlike popular programs such as Excel consistently
gives the correct answer.  If you go for freeware, you run the risk
of generating an erroneous result.

3.  Jochen
http://www.netlib.org

4.  Roy Jensen
Excel and Quattro Pro can fit to non-linear functions. They are not free but 
you probably have one on your computer. I have found the Excel Solver to be 
very stable.

There are several J. Chem. Ed. articles that outline the procedure.
Mark Iannone, September 98, 1188.
Robert de Levie, November 99, 1594.
Harris, Vol 75, 1998, 119.

5.  Tom Kuppens
You could try CurveExpert. It's fully fuctional shareware (WIN**).
You can find it at a simtel ftp or at www.download.com.

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From: Tom Hawkins <[email-masked]>
Date: Fri, 28 Apr 2000 16:37:17 +0100

>very stable.

I use Excel's Solver to fit power curves (y=ax^b) to experimental data by
minimising SSE and find it sometimes produces far from optimal solutions,
even though it believes convergence was achieved. Tweaking the parameters
>from their defaults helps but I still haven't got it 100% reliable. The
problem is related to the magnitude of the data, i.e. data sets with x
values above a certain value consistently don't work. I'd recommend thorough
testing of any fitting routine you develop using Solver!

Alternatively, if anyone has a good suggestion as to what I might be doing
wrong, I'd be very interested to hear it...

Dr Tom Hawkins             Osmetech plc
Sensor Technologist        Electra House, Electra Way, Crewe CW1 6WZ
[email-masked]   Tel +44(0)1270 216444 Fax +44(0)1270 216030