3,795 research outputs found
Filtering Algorithms for the Multiset Ordering Constraint
Constraint programming (CP) has been used with great success to tackle a wide
variety of constraint satisfaction problems which are computationally
intractable in general. Global constraints are one of the important factors
behind the success of CP. In this paper, we study a new global constraint, the
multiset ordering constraint, which is shown to be useful in symmetry breaking
and searching for leximin optimal solutions in CP. We propose efficient and
effective filtering algorithms for propagating this global constraint. We show
that the algorithms are sound and complete and we discuss possible extensions.
We also consider alternative propagation methods based on existing constraints
in CP toolkits. Our experimental results on a number of benchmark problems
demonstrate that propagating the multiset ordering constraint via a dedicated
algorithm can be very beneficial
Solving Set Constraint Satisfaction Problems using ROBDDs
In this paper we present a new approach to modeling finite set domain
constraint problems using Reduced Ordered Binary Decision Diagrams (ROBDDs). We
show that it is possible to construct an efficient set domain propagator which
compactly represents many set domains and set constraints using ROBDDs. We
demonstrate that the ROBDD-based approach provides unprecedented flexibility in
modeling constraint satisfaction problems, leading to performance improvements.
We also show that the ROBDD-based modeling approach can be extended to the
modeling of integer and multiset constraint problems in a straightforward
manner. Since domain propagation is not always practical, we also show how to
incorporate less strict consistency notions into the ROBDD framework, such as
set bounds, cardinality bounds and lexicographic bounds consistency. Finally,
we present experimental results that demonstrate the ROBDD-based solver
performs better than various more conventional constraint solvers on several
standard set constraint problems
Well Structured Transition Systems with History
We propose a formal model of concurrent systems in which the history of a
computation is explicitly represented as a collection of events that provide a
view of a sequence of configurations. In our model events generated by
transitions become part of the system configurations leading to operational
semantics with historical data. This model allows us to formalize what is
usually done in symbolic verification algorithms. Indeed, search algorithms
often use meta-information, e.g., names of fired transitions, selected
processes, etc., to reconstruct (error) traces from symbolic state exploration.
The other interesting point of the proposed model is related to a possible new
application of the theory of well-structured transition systems (wsts). In our
setting wsts theory can be applied to formally extend the class of properties
that can be verified using coverability to take into consideration (ordered and
unordered) historical data. This can be done by using different types of
representation of collections of events and by combining them with wsts by
using closure properties of well-quasi orderings.Comment: In Proceedings GandALF 2015, arXiv:1509.0685
On Formal Consistency between Value and Coordination Models
In information systems (IS) engineering dierent techniques for modeling
inter-organizational collaborations are applied. In particular, value models
estimate the profitability for involved stakeholders, whereas coordination models
are used to agree upon the inter-organizational processes before implementing
them. During the execution of inter-organizational collaboration, in addition, event
logs are collected by the individual organizations representing another view of the
IS. The combination of the two models and the event log represent the IS and they
should therefore be consistent, i.e., not contradict each other. Since these models
are provided by dierent user groups during design time and the event log is
collected during run-time consistency is not straight forward. Inconsistency occurs
when models contain a conflicting description of the same information, i.e.,
there exists a conflicting overlap between the models. In this paper we introduce
an abstraction of value models, coordination models and event logs which allows
ensuring and maintaining alignment between models and event log. We demonstrate
its use by outlining a proof of an inconsistency resolution result based on
this abstraction. Thus, the introduction of abstractions allows to explore formal
inter-model relations based on consistency
Violator Spaces: Structure and Algorithms
Sharir and Welzl introduced an abstract framework for optimization problems,
called LP-type problems or also generalized linear programming problems, which
proved useful in algorithm design. We define a new, and as we believe, simpler
and more natural framework: violator spaces, which constitute a proper
generalization of LP-type problems. We show that Clarkson's randomized
algorithms for low-dimensional linear programming work in the context of
violator spaces. For example, in this way we obtain the fastest known algorithm
for the P-matrix generalized linear complementarity problem with a constant
number of blocks. We also give two new characterizations of LP-type problems:
they are equivalent to acyclic violator spaces, as well as to concrete LP-type
problems (informally, the constraints in a concrete LP-type problem are subsets
of a linearly ordered ground set, and the value of a set of constraints is the
minimum of its intersection).Comment: 28 pages, 5 figures, extended abstract was presented at ESA 2006;
author spelling fixe
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