Improving fit of custom function

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Romio
Romio 2020-8-10
评论： Rena Berman 2020-10-12
Hello,
I have the following curve.
I want to fit it into a closed-form equation. I tried to use GRABIT to get a vector of values that could plot it.
x = [0.0194119350975558 0.248031785422458 0.291351961297183 0.334455968629621 0.397706884103397 0.439513880182100 0.459876956865727 0.644744294231326 0.658622314646282 0.755249653049490 0.832378588938224 0.889360616685617 0.929005927341429 0.970164417793265 0.990095157392316 1.05248139869694 1.11508380854384 1.20042714903956 1.24439583054116 1.26670442410539 1.33211702500205 1.40033981694848 1.46964345160635 1.56039100565929 1.58464511610412 1.60738604675293 1.67279864764960 1.73734657437711 1.84391766572561 1.92839633205217 1.99143107898366 2.07482890259878 2.26069061525890 2.34387227033173 2.42813476811600 2.53492202800680 2.62113004267167 2.70712188879425 2.73029515652764 2.81693550827709 2.88234810917376 2.98956770614913 3.07491104664485 3.18169830653564 3.28783706079956 3.47910298701692 9.89096458726940]
y = [0.382895015585752 0.936494005646322 0.944570062386241 0.950609811457797 0.946433435220773 0.940255338282152 0.932075520641934 0.473525838625860 0.404256790934756 0.314486318692959 0.241040894764830 0.177811596145283 0.151270422523033 0.138983402579323 0.126730969602380 0.114409362691904 0.104124063449791 0.108058330919451 0.122243310664459 0.132390262039507 0.148576962486111 0.191235662621433 0.244075901098568 0.298917860277301 0.327391580667615 0.341611147379389 0.357797847825993 0.365839317599146 0.369738998102040 0.365528034898250 0.359315350992862 0.344922849447257 0.295740182705652 0.279311373491684 0.273064102619530 0.279000090790788 0.291079588933900 0.301122779408649 0.319414961457149 0.335567074936987 0.351753775383591 0.361762378891574 0.365696646361235 0.371632634532492 0.371459699698661 0.373184724666128 0.372920999044535]
However, I am trying to fit that into an equation, whatever it is. Is that possible? If so, how can I do that
Thanks,
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Walter Roberson
Walter Roberson 2020-8-12
No, Alex just reported the software he is using when you asked; he did not say it is free.
Alex has posted responses to a number of optimization / fitting questions over the last couple of years, making use of that software to find values. I do sometimes find better values than that software obtains, but the software is producing outputs within a quite small number of minutes, whereas it may take me several hours of work to locate an improved point. For people who do a lot of fitting or optimization, it appears to me that the software he is using is good value for the price. But, Yes, it does cost a fair bit, and Yes, that does effectively act to keep most students from using that other software.

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回答（1 个）

Sulaymon Eshkabilov
Hi,
Why not to use cftool (Curve Fitting Toolbox).
  1. Launch it with: >> cftool
  2. Indicate your x data and y data variable names in GUI window of cftool
  3. Select the available fit models or enter your custom equation
Good luck.

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