Statistical - Cubic Regression (Cubic Spline Fit) ?

[jte]

I implemented cubic fit routines for the HP Prime’s Function app’s “sketch a function” feature, but those routines are only available via the “sketch a function” interface.

Ideally, numerical round-off should be taken into account when implementing these sorts of routines. As it was practical for this problem, I used an arithmetic with enough precision to allow for the calculations to be performed without any numerical round-off. (The input to these cubic fit routines are points with bounded integer coordinates — points from touch input. This limits the general applicability of the “sketch a function” cubic fit routines in the Prime.)