20,103 research outputs found
Non-blocking supervisory control for initialised rectangular automata
We consider the problem of supervisory control for a class of rectangular automata and more specifically for compact rectangular automata with uniform rectangular activity, i.e. initialised. The supervisory controller is state feedback and disables discrete-event transitions in order to solve the non-blocking forbidden state problem. The non-blocking problem is defined under both strong and weak conditions. For the latter maximally permissive solutions that are computable on a finite quotient space characterised by language equivalence are derived
Area-Universal Rectangular Layouts
A rectangular layout is a partition of a rectangle into a finite set of
interior-disjoint rectangles. Rectangular layouts appear in various
applications: as rectangular cartograms in cartography, as floorplans in
building architecture and VLSI design, and as graph drawings. Often areas are
associated with the rectangles of a rectangular layout and it might hence be
desirable if one rectangular layout can represent several area assignments. A
layout is area-universal if any assignment of areas to rectangles can be
realized by a combinatorially equivalent rectangular layout. We identify a
simple necessary and sufficient condition for a rectangular layout to be
area-universal: a rectangular layout is area-universal if and only if it is
one-sided. More generally, given any rectangular layout L and any assignment of
areas to its regions, we show that there can be at most one layout (up to
horizontal and vertical scaling) which is combinatorially equivalent to L and
achieves a given area assignment. We also investigate similar questions for
perimeter assignments. The adjacency requirements for the rectangles of a
rectangular layout can be specified in various ways, most commonly via the dual
graph of the layout. We show how to find an area-universal layout for a given
set of adjacency requirements whenever such a layout exists.Comment: 19 pages, 16 figure
Roots, symmetries and conjugacy of pseudo-Anosov mapping classes
An algorithm is proposed that solves two decision problems for pseudo-Anosov
elements in the mapping class group of a surface with at least one marked fixed
point. The first problem is the root problem: decide if the element is a power
and in this case compute the roots. The second problem is the symmetry problem:
decide if the element commutes with a finite order element and in this case
compute this element. The structure theorem on which this algorithm is based
provides also a new solution to the conjugacy problem
The Temporal Logic of two dimensional Minkowski spacetime is decidable
We consider Minkowski spacetime, the set of all point-events of spacetime
under the relation of causal accessibility. That is, can access if an electromagnetic or (slower than light) mechanical signal could be
sent from to . We use Prior's tense language of
and representing causal accessibility and its converse relation. We
consider two versions, one where the accessibility relation is reflexive and
one where it is irreflexive.
In either case it has been an open problem, for decades, whether the logic is
decidable or axiomatisable. We make a small step forward by proving, for the
case where the accessibility relation is irreflexive, that the set of valid
formulas over two-dimensional Minkowski spacetime is decidable, decidability
for the reflexive case follows from this. The complexity of either problem is
PSPACE-complete.
A consequence is that the temporal logic of intervals with real endpoints
under either the containment relation or the strict containment relation is
PSPACE-complete, the same is true if the interval accessibility relation is
"each endpoint is not earlier", or its irreflexive restriction.
We provide a temporal formula that distinguishes between three-dimensional
and two-dimensional Minkowski spacetime and another temporal formula that
distinguishes the two-dimensional case where the underlying field is the real
numbers from the case where instead we use the rational numbers.Comment: 30 page
Revisiting Numerical Pattern Mining with Formal Concept Analysis
In this paper, we investigate the problem of mining numerical data in the
framework of Formal Concept Analysis. The usual way is to use a scaling
procedure --transforming numerical attributes into binary ones-- leading either
to a loss of information or of efficiency, in particular w.r.t. the volume of
extracted patterns. By contrast, we propose to directly work on numerical data
in a more precise and efficient way, and we prove it. For that, the notions of
closed patterns, generators and equivalent classes are revisited in the
numerical context. Moreover, two original algorithms are proposed and used in
an evaluation involving real-world data, showing the predominance of the
present approach
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