Timeline for Why does FindFit work and NonlinearModelFit does not?
Current License: CC BY-SA 3.0
5 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Oct 11, 2015 at 2:52 | comment | added | xzczd♦ |
@jud Change the definition of the function to myfunction[t_?NumericQ, qi_?NumericQ, di_?NumericQ, b_?NumericQ, dt_?NumericQ] will suppress the Warning. (Remember to Clear@myfunction first. ) This issue has been addressed for several times before, just search in this site for more details.
|
|
| Aug 17, 2015 at 22:33 | comment | added | Jud | Thank you all for the responses. A couple things to note: the constraints are important. This is an engineering equation and the theoretical physics fail if left to regress to numbers outside of those bounds. I also realize now, that there was not a problem all along with the regression with the output I got before, I still could get the parameters the way that @JimB has described. I had tried something similar to nlm[5], and because that failed, I thought there was a problem. But the regression still worked. I feel like an idiot now for not trying that. Thanks again. | |
| Aug 17, 2015 at 19:55 | comment | added | JimB | @MarcoB. I agree. And the extreme serial correlation in the residuals should also cause some concern but I've noticed that such deviations in residual behavior (or local lack of fit) tends to be tolerated or ignored at this site. | |
| Aug 17, 2015 at 19:50 | comment | added | MarcoB |
Note also that the value of the di parameter is essentially unchanged in the optimization. If you use a different starting value, the same value will be returned by the fit. @Jud should really rethink his model thoroughly.
|
|
| Aug 17, 2015 at 19:28 | history | answered | JimB | CC BY-SA 3.0 |