I have a set of point x and y and I would like to find the best (polynomial?) fit and store it so that I can use it as a function. Polynomials.jl creates the fit but not the function (evaluating the function at a point inside the relevant range delivers wrong results). What’s a good package and a …

Polynomials.jl should produce good numbers - could you post a snippet that reproduces the case where you get incorrect results?

Apologies, Polynomials works. If the order of the Polynomial is not specified and the vector is too large (about 300 points) the fit is created but the predicted values are crazy. With polynomials of smaller orders, like 5, 10, 50, the results are sensible. There is just no warning, that could be fi…

This is Runge’s phenomenon , as well as the inherent ill-conditionedness of fitting a polynomial whose degree is close to the number of control points. If you can choose the sampling points, it’s common to use Chebyshev node spacing to mitigate the ringing effect. If you don’t actually need to fit a…

You could also fit your data with a spline, which would avoid Runge’s phenomenon. See this previous post for an example using BSplineKit.jl .

Radial Basis Functions are also a good choice.

You might find the ArnoldiFit method in Polynomials a better choice when the vector is “too large”: fit(ArnoldiFit, x, y, ...)

Package for fitting a curve and storing the function

General Usage

jling August 10, 2021, 2:12pm 2

LsqFit.jl?

Topic		Replies	Views
How to fit a polynomial with a pre-determined degree to a set of points? General Usage regression , fit , curve-fitting , polynomials , approxfun	7	2502	December 27, 2022
Polynomial problem-help me please New to Julia question , homework	8	640	October 19, 2023
Overfitting polynomial. help New to Julia question , homework	3	351	October 19, 2023
Fitting a polynomial of degree 10 to data General Usage data , regression , polynomials	9	3465	November 4, 2021
Data approximation with a curve Numerics question , package	18	5096	October 18, 2018

Package for fitting a curve and storing the function

Related topics