Data smoothing algorithms?

[John J. Lee]

"Anthra Norell" <anthra.norell at tiscalinet.ch> writes:

> Hi,
> 
> The following are differences of solar declinations from one day to
> the next, (never mind the unit). Considering the inertia of a
> planet, any progress of (apparent) celestial motion over regular
> time intervals has to be highly regular too, meaning that a plot
> cannot be jagged. The data I googled out of Her Majesty's Nautical
> Almanac are merely nautical precision and that, I suppose, is where
> the jitter comes in. There's got to be algorithms out there to iron
> it out. If it were a straight line, I could do it. But this, over
> the whole year, is a wavy curve, somthing with a dominant sine
> component. Suggestions welcome.

The important thing is to have a (mathematical, hopefully) model of
how you expect the data to vary with time.  Start from there, and
then, for example, use regression to fit a curve to the data.

The "Numerical Recipes" (Press et al.) book is popular and IMHO is a
good place to learn about these things (comes in several language
flavours, including Fortran and C -- sadly no Python AFAIK), though
the implementations aren't a great choice for serious "production"
use, according to those in the know.

OTOH, there are quick and dirty methods that don't involve any model
worth speaking of -- and Press et al. covers those too :-)


John