>Hey Lawrence,
>
>non-linear curve fitting is not so bad as you think. The finest program
>I've ever seen (and a had a lot of...) is the NLREGR v 3.4 available from
>Simtel (I mean downloadable). Knowing the matter, it is very stable and
>reliable. You could also some things from the Linux/GNU scene: e. g.
>FUDGIT or GNUPLOT (it can also fit even if it could be fooled). The point
>is at the curve fitting: one must have a good idea how the curve looks (I
>mean the term of the curve) and one should guess the initial parametes (e.
>g. using mean calculation or linear regression). I dealt a lot of
>thermistors and other beasts (e. g. rotating valve: describe the amount of
>fluid depending on the opening angle - not a nice curve I promise).
>
>The bad news is that in most cases floating point arithmetic is needed.
>
>I hope this helps.
>
>Imre
>
>PS: If you want only interpolate based on given points and you are not
>interested in the formula of the WHOLE curve that is a completely
>different matter. If u want things simple (but relatively good) use
>Newton's divided difference method. If u want to go as precise as possible
>there is only one winner: the SPQS method to be found in Netlib. However
>it is a several 10k of FORTRAN code (I put it onto awk and Euphoria, too).
>This tool is a bless!
>
>
>On Fri, 15 Nov 2002
RemoveMEllileEraseMEEraseMESALTONUSA.COM wrote:
>
> > That's one way to deal with it.
> >
> > A typical problem for me is interpolating thermistor data. The thermistor
> > curve comes in chart form from the manufacturer, in very un-handy
> > increments. It's quite a complex curve, and I think curve fitting it
> > would be a long involved task (unless Excel does this automatically
> > somehow? ) Linear curve fitting would be a cinch. The only way I know
> > how to curve fit a nonlinear is, guess at the type of equation to use,
> > plot it next to your data, sum the squares of the differences, then run a
> > linear regression on the results and use a Tools:GoalSeek on the results
> > to approach the minimum, then guess again at the type of equation to use
> > until you like the fit.. It is a time-consuming process, usually.
> >
> > Is there a more efficient way?
> >
> >
> > -- Lawrence Lile
> >
> >
> >
> >
> >
> >
> >
> > "Gordon Williams" <
RemoveMEg_willspam_OUTKILLspamcyberus.ca>
> > 11/15/02 01:21 PM
> >
> >
> > To: <
RemoveMEllileTakeThisOuTspamSALTONUSA.COM>
> > cc:
> > Subject: Re: Re: [EE]:Pressure sensor confusion
> >
> >
> > The way that I usually handle it is to plot the experimental data, put my
> > choice of curve fit on the graph and have it show the equation for the
> > curve.
> >
> > The equation then can be used for interpolation or extrapolation.
> >
> > Gordon Williams
> >
> > --
> >
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http://www.piclist.com/#archives for details.
> >
> >
> >
>
>--
>
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