On Tue, 24 Jun 2008, IOhannes m zmoelnig wrote:
true that "4" doesn't say much about the interpolation alogrithm and
that is definitely a weakness in the current naming scheme.
Well, I'd have expected "4" to be a cubic spline algorithm, because it
uses a sliding window of 4 samples, polynomial interpolation is pretty
much the default, 4-point polynomial leads to cubic curves (using Lagrange
or not), and beyond having a continuous curve (C0) and continuous
derivative (C1), it's also nice to have a continuous second-derivative
(C2). All this leading to basically one specific formula, which [tabread4]
doesn't use, but which I assumed [tabread4] was using, until Roman told me
that Cyrille had looked at it closely and found it to be non-C1.
(I made a mistake while talking to Roman. I said it's only C1, but the
thing is that first derivatives are the last derivatives to be chosen
according to samples. Second derivatives are chosen so that they fall to
zero at every junction of pieces, and never anything else than zero. It's
like that because there are 4 degrees of freedom, which are used up for
start & end points of f & f'... that's 4, so f''(0) and f''(1) can't be
set by variables... but it can be set by constants.)
All this to say that I don't think that the current interpolator deserved
to be called THE "4", because there's a more generally useful interpolator
that uses up the same power and thus would've been a much better choice
for a default. The point of a default value or default algorithm is so
that you need to specify a non-default as seldom as possible, and an
unqualified "4" looks like a default to me (the name of the algorithm is
implied)
it, however, was my intention to say that [tabread_tweak~] is one of the
worst possible names i could think of. i do not say that this is is
"constructive" criticism, rather i meant it as a preventive criticism.
It's like the names of the codecs in Quicktime-related GUIs... they all
come out with different names than what the rest of the world is calling
them... I don't have any names off the top of my head anymore, but it sure
is/was confusing.
_ _ __ ___ _____ ________ _____________ _____________________ ...
| Mathieu Bouchard - tél:+1.514.383.3801, Montréal, Québec
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