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Subject: Re: improvements for interpolation in charts

Hi Regina,

On Thu, 2011-11-10 at 12:32 -0700, Regina Henschel wrote:
> Hi all,
> I have noticed, that you are discussing improvements for interpolations 
> in charts. Currently both kind of interpolations are parametric. That 
> gives nice curves, but for some functions the result can be better with 
> non-parametric methods. So I want to see non-parametric interpolation 
> methods in addition. For example my textbook "Engeln-Müllges, Gisela: 
> Numerik-Algorithmen" suggests the "Akima Subsplines" for not smooth 
> functions. It should be possible to use such interpolations too.

In fact they should be relatively easy to implement. I'll put them on
the list of interpolation methods to define (hopefully for 1.3).
> If the already made suggestion "fixed derivatives at both ends" includes 
> "non-parametric" too, I would second that kind.
> I do not find the term "parabolic limits" besides in the description of 
> the application "goffice". What does it mean? Is it the same as 
> "parabolically terminated"? And what does "cubic limits" mean?
> [I'm no professional mathematician, but will implement those 
> interpolations. So please excuse me, if my questions are stupid.]

I really don't yet what specifically these methods are. I still have to
analyse the goffice code to see what they are calculating, determine
whether these are mathematically reasonable (and standard (in the sense
of "accepted in the field") and then write them down in a way that
non-mathematicians can implement them. I'll let you know when I have a
first draft.

Andreas J. Guelzow, PhD, FTICA
Concordia University College of Alberta

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