Show HN: An easy-to-use online curve fitting tool

https://byx2000.github.io/curve-fit/

by byx • 9 months ago

35 15 9 months ago

byx2000.github.io

This is a powerful online curve fitting tool that supports fitting dozens of commonly used functions and implicit functions. It features a clean interface and simple operation. If you need to perform curve fitting but don't want to learn professional software like Matlab or Origin, you can try this tool.

okramcivokram2• 8 months ago

It'd be nice if there was some demo data because I might want to play with it to see how it works, but don't have any data to use it on.

okramcivokram2• 8 months ago

I've now tried it by adding a bunch of random points and I find it very cool! It can make curves fit very snugly. Maybe enhance it by a mode that runs all the models and shows you which one has the least errors/best fit.

cb3212• 8 months ago

The fit diagnostics at the top of the plot are inadequate. This needs at a minimum error estimates on the estimated parameters (probably bootstrap) and ideally some kind of "error envelope" on the plot.

indeed303• 8 months ago

I don’t think you can do anything sensible here without making much stronger modelling assumptions. A vanilla non-parametric bootstrap is only valid under a very specific generative story: IID sampling from a population. Many (most?) curve-fitting problems won't satisfy that.

For example, suppose you measure the decay of a radioactive source at fixed times t = 0,1,2,... and fit y = A e^{-kt}. The only randomness is small measurement error with, say, SD = 0.5. The bootstrap sees the huge spread in the y-values that comes from the deterministic decay curve itself, not from noise. It interprets that structural variation as sampling variability and you end up with absurdly wide bootstrap confidence intervals that have nothing to do with the actual uncertainty in the experiment.

abdullahkhalids2• 8 months ago

What methods can you use the estimate the standard error in this case?

cb3212• 8 months ago

These are all big topics, but any "parametric curve fitting" like this tool uses is parameter estimation (the parameters of the various curves). That already makes strong modeling assumptions (usually including IID, Gaussian noise, etc.,) to get the parameter estimates in the first place. I agree it would be even better to have ways to input measurement errors (in both x- & y- !) per your example and have non-bootstrap options (I only said "probably"), residual diagnostics, etc.

Maybe a residuals plot and IID tests of residuals (i.e. tests of some of the strong assumptions!) would be a better next step for the author than error estimates, but I stand by my original feedback. Right now even the simplest case of a straight line fit is reported with only exact slope & intercept (well, not exact, but to an almost surely meaningless 16 decimals!), though I guess he thought to truncate the goodness of fit measures at ~4 digits.

iSpiderman• 8 months ago

Very nice. I will use this at school to quickly produce fits. File import does not seem to work though...

byx• 8 months ago

Thanks for the feedback, this bug has been fixed.

monkeydust• 8 months ago

Pretty sure this could replace one of my junior quants!

abdullahkhalids2• 8 months ago

Would be very nice if I could copy-paste data straight from a spreadsheet software.

murphyslab2• 8 months ago

Copy-paste worked perfectly for me. I just copied 16 data points I had in an open G Sheets tab and used the "Batch Add" button.

murphyslab2• 8 months ago

Not to cast shade, but it looks like you've essentially built a front-end for Desmos. It definitely makes things faster than trying to do it directly in Desmos.

Suggestion: Most of the fits that you've done assume that the errors are normally distributed. It would be worthwhile adding some graphical or numerical checks on that, rather than having goodness of fit or visual inspection be the only indication if this is a faulty assumption.

It gave made for a good quick check testing some data I had.

doppelgunner• 8 months ago

Hey,

I really like your tool and thought you might enjoy sharing it on NextGen Tools, a Product Hunt alternative: https://nxgntools.com

I’d appreciate any feedback and would love to hear your thoughts.

Show HN: An easy-to-use online curve fitting tool

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