Motion 11
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Dear George, Dan, and intervallers,
Motion 11 appears unique among all already discussed stds-1788 motions
in that it has, so far, led to almost no debate at all on this list. As
I understand it, the discussion period has been extended due to the lack
of discussion leading to some consensus, not because the debate was too
heated to reach a consensus in the allotted time.
Why such an apathy? I believe it is because many on this list do not see
the point of reverse operators for lack of familiarity with its
applications. Marco Nehmeier took the time to write Motion 11, and for
that I thank him. However, I now believe that Motion 11, as written now,
does a significant disservice to reverse operators in presenting only
the basic ones. I fear that to the majority, reverse operators are now
but a tricky way to present an extended division useful to perform
Newton steps. In addition, as I have already pointed out twice, Motion
11's wrong Corollary 1 gives the impression that n+1-ary reverse
operators can be expressed in terms of n-ary reverse operators, which
they cannot without unreasonably enlarging the computed intervals.
In the constraint programming community, reverse operators are central
to many algorithms that work great to prune domains when they are large,
and they have been used with great success on some challenging problems
(see for instance: "Progress in the Solving of a Circuit Design
Problem", L. Granvilliers & F. Benhamou, J. Global Opt., 20(2), 2001).
In robotics, they are at the heart of several important algorithms (see,
e.g., Luc Jaulin's papers at
http://www.ensieta.fr/jaulin/publications.html).
Reverse operators are an important tool, and there is more, much more to
it than extended division.
Can reverse operators be implemented from operations already in the
standard? No, they cannot. At least not without sacrificing performances
beyond the reasonable.
I believe with George Corliss that we should keep the standard as simple
as possible. I voiced my dissent on some previous motions with that same
argument. However, supporting reverse operators adds operators to the
standard, not complexity. Supporting decorated intervals, that is
something that added complexity.
What now? I believe that the absence of debate over Motion 11 so far
reflects an absence of interested parties on the list. I am therefore in
favor of having Marco Nehmeier withdraw his motion for the time being,
and resubmit a new extended motion that presents all reverse operators,
together with a document presenting convincing rationales in favor of
their introduction into the standard. Let all people on the list
understand the possible benefits of having reverse operators before
voting on their adoption.
F.
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Frédéric Goualard LINA - UMR CNRS 6241
Tel.: +33 2 51 12 58 38 Univ. of Nantes - Ecole des Mines de Nantes
Fax.: +33 2 51 12 58 12 2, rue de la Houssinière - BP 92208
http://goualard.frederic.free.fr/ F-44322 NANTES CEDEX 3
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