Which reminds me, there is a nifty tool called fityk that I tend to use just to view graphs, but has a rather nice set of routines to do various fits to various curves.
Cheers, Magnus On 10/07/2013 09:46 AM, Ulrich Bangert wrote: > Jim, > > most if not all fitting strategies make use of an assumption concerning the > underlying model. > > For those who are not sure what the underlying model is this one > > http://creativemachines.cornell.edu/eureqa > > is the hottest tool that I have ever seen. Give it a try. > > Best regards > > Ulrich > >> -----Ursprungliche Nachricht----- >> Von: [email protected] >> [mailto:[email protected]] Im Auftrag von Jim Lux >> Gesendet: Freitag, 4. Oktober 2013 19:38 >> An: Discussion of precise time and frequency measurement >> Betreff: [time-nuts] exponential+linear fit >> >> >> I'm trying to find a good way to do a combination >> exponential/linear fit >> (for baseline removal). It's modeling phase for a moving >> source plus a >> thermal transient, so the underlying physics is the linear term (the >> phase varies linearly with time, since the velocity is constant) plus >> the temperature effect. >> >> the general equation is y(t) = k1 + k2*t + k3*exp(k4*t) >> >> Working in matlab/octave, but that's just the tool, I'm >> looking for some >> numerical analysis insight. >> >> I could do it in steps.. do a straight line to get k1 and k2, >> then fit >> k3& k4 to the residual; or fit the exponential first, then do the >> straight line., but I'm not sure that will minimize the >> error, or if it >> matches the underlying model (a combination of a linear trend and >> thermal effects) as well. >> >> I suppose I could do something like do the fit on the >> derivative, which >> would be >> >> y'(t) = k2 + k3*k4*exp(k4*t) >> >> Then solve for the the k1. In reality, I don't think I care as much >> what the numbers are (particularly the k1 DC offset) so >> could probably >> just integrate (numerically) >> >> y'()-k2-k3*k4*exp(k4*t) and get my sequence with the DC term, linear >> drift, and exponential component removed. >> >> >> The fear I have is that differentiating emphasizes noise. >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
