438,427 research outputs found
Experimental Evaluation of Branching Schemes for the CSP
The search strategy of a CP solver is determined by the variable and value
ordering heuristics it employs and by the branching scheme it follows. Although
the effects of variable and value ordering heuristics on search effort have
been widely studied, the effects of different branching schemes have received
less attention. In this paper we study this effect through an experimental
evaluation that includes standard branching schemes such as 2-way, d-way, and
dichotomic domain splitting, as well as variations of set branching where
branching is performed on sets of values. We also propose and evaluate a
generic approach to set branching where the partition of a domain into sets is
created using the scores assigned to values by a value ordering heuristic, and
a clustering algorithm from machine learning. Experimental results demonstrate
that although exponential differences between branching schemes, as predicted
in theory between 2-way and d-way branching, are not very common, still the
choice of branching scheme can make quite a difference on certain classes of
problems. Set branching methods are very competitive with 2-way branching and
outperform it on some problem classes. A statistical analysis of the results
reveals that our generic clustering-based set branching method is the best
among the methods compared.Comment: To appear in the 3rd workshop on techniques for implementing
constraint programming systems (TRICS workshop at the 16th CP Conference),
St. Andrews, Scotland 201
Growth Velocities of Branched Actin Networks
The growth of an actin network against an obstacle that stimulates branching
locally is studied using several variants of a kinetic rate model based on the
orientation-dependent number density of filaments. The model emphasizes the
effects of branching and capping on the density of free filament ends. The
variants differ in their treatment of side vs. end branching and
dimensionality, and assume that new branches are generated by existing branches
(autocatalytic behavior) or independently of existing branches (nucleation
behavior). In autocatalytic models, the network growth velocity is rigorously
independent of the opposing force exerted by the obstacle, and the network
density is proportional to the force. The dependence of the growth velocity on
the branching and capping rates is evaluated by a numerical solution of the
rate equations. In side-branching models, the growth velocity drops gradually
to zero with decreasing branching rate, while in end-branching models the drop
is abrupt. As the capping rate goes to zero, it is found that the behavior of
the velocity is sensitive to the thickness of the branching region. Experiments
are proposed for using these results to shed light on the nature of the
branching process.Comment: 6 figure
Combinatorics of branchings in higher dimensional automata
We explore the combinatorial properties of the branching areas of execution
paths in higher dimensional automata. Mathematically, this means that we
investigate the combinatorics of the negative corner (or branching) homology of
a globular -category and the combinatorics of a new homology theory
called the reduced branching homology. The latter is the homology of the
quotient of the branching complex by the sub-complex generated by its thin
elements. Conjecturally it coincides with the non reduced theory for higher
dimensional automata, that is -categories freely generated by
precubical sets. As application, we calculate the branching homology of some
-categories and we give some invariance results for the reduced
branching homology. We only treat the branching side. The merging side, that is
the case of merging areas of execution paths is similar and can be easily
deduced from the branching side.Comment: Final version, see
http://www.tac.mta.ca/tac/volumes/8/n12/abstract.htm
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