Statistical - Cubic Regression (Cubic Spline Fit) ?

[Gjermund Skailand]

This is a bit off topic as there is no regression involved,
https://people.maths.ox.ac.uk/trefethen/barycentric.pdf

but Barycentric Lagrange interpolation is a numerically stable interpolation method which fits to all points of (large) datasets and can be used for interpolation and also for derivatives.

https://www.hpcalc.org/hp49/math/numeric/chebhp50.zip
included in hpgcc3 for the hp50g only.
br Gjermund