Look at http://www.mfsoft.com/equationgrapher/index.html for an inexpensive package - it's got a free trial period. I've played with it, and it works. Larry At 03:48 PM 11/16/2002 +0100, you wrote: >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 llile@SALTONUSA.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" > > 11/15/02 01:21 PM > > > > > > To: > > 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 > > > > -- > > http://www.piclist.com hint: The PICList is archived three different > > ways. See http://www.piclist.com/#archives for details. > > > > > > > >-- >http://www.piclist.com#nomail Going offline? Don't AutoReply us! >email listserv@mitvma.mit.edu with SET PICList DIGEST in the body Larry Bradley Orleans (Ottawa), Ontario, CANADA -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body