520 research outputs found
Self-tuning algorithms for the assignment of packet control units and handover parameters in GERAN
Esta tesis aborda el problema de la optimización automática de parámetros en redes de acceso radio basadas en GSM-EDGE Radio Access Network (GERAN). Dada la extensión del conjunto de parámetros que se puede optimizar, este trabajo se centra en dos de los procesos encargados de la gestión de la movilidad: el proceso de (re)selección de celda para servicios por conmutación de paquetes y el proceso de traspaso para servicios de voz por conmutación de circuitos
Acyclic partitioning of large directed acyclic graphs
We investigate the problem of partitioning the vertices of a directed acyclic
graph into a given number of parts. The objective function is to minimize the number or the
total weight of the edges having end points in different parts, which is also known as edge
cut. The standard load balancing constraint of having an equitable partition of the vertices
among the parts should be met. Furthermore, the partition is required to be acyclic, i.e.,
the inter-part edges between the vertices from different parts should preserve an acyclic
dependency structure among the parts. In this work, we adopt the multilevel approach with
coarsening, initial partitioning, and refinement phases for acyclic partitioning of directed
acyclic graphs. We focus on two-way partitioning (sometimes called bisection), as this
scheme can be used in a recursive way for multi-way partitioning. To ensure the acyclicity
of the partition at all times, we propose novel and efficient coarsening and refinement
heuristics. The quality of the computed acyclic partitions is assessed by computing the
edge cut. We also propose effective ways to use the standard undirected graph partitioning
methods in our multilevel scheme. We perform a large set of experiments on a dataset
consisting of (i) graphs coming from an application and (ii) some others corresponding
to matrices from a public collection. We report improvements, on average, around 59%
compared to the current state of the art
Graph partitioning using matrix values for preconditioning symmetric positive definite systems
Prior to the parallel solution of a large linear system, it is required to
perform a partitioning of its equations/unknowns. Standard partitioning
algorithms are designed using the considerations of the efficiency of the
parallel matrix-vector multiplication, and typically disregard the information
on the coefficients of the matrix. This information, however, may have a
significant impact on the quality of the preconditioning procedure used within
the chosen iterative scheme. In the present paper, we suggest a spectral
partitioning algorithm, which takes into account the information on the matrix
coefficients and constructs partitions with respect to the objective of
enhancing the quality of the nonoverlapping additive Schwarz (block Jacobi)
preconditioning for symmetric positive definite linear systems. For a set of
test problems with large variations in magnitudes of matrix coefficients, our
numerical experiments demonstrate a noticeable improvement in the convergence
of the resulting solution scheme when using the new partitioning approach
An Efficient Paradigm for Feasibility Guarantees in Legged Locomotion
Developing feasible body trajectories for legged systems on arbitrary
terrains is a challenging task. Given some contact points, the trajectories for
the Center of Mass (CoM) and body orientation, designed to move the robot, must
satisfy crucial constraints to maintain balance, and to avoid violating
physical actuation and kinematic limits. In this paper, we present a paradigm
that allows to design feasible trajectories in an efficient manner. In
continuation to our previous work, we extend the notion of the 2D feasible
region, where static balance and the satisfaction of actuation limits were
guaranteed, whenever the projection of the CoM lies inside the proposed
admissible region. We here develop a general formulation of the improved
feasible region to guarantee dynamic balance alongside the satisfaction of both
actuation and kinematic limits for arbitrary terrains in an efficient manner.
To incorporate the feasibility of the kinematic limits, we introduce an
algorithm that computes the reachable region of the CoM. Furthermore, we
propose an efficient planning strategy that utilizes the improved feasible
region to design feasible CoM and body orientation trajectories. Finally, we
validate the capabilities of the improved feasible region and the effectiveness
of the proposed planning strategy, using simulations and experiments on the HyQ
robot and comparing them to a previously developed heuristic approach. Various
scenarios and terrains that mimic confined and challenging environments are
used for the validation.Comment: 17 pages, 13 figures, submitted to Transaction on Robotic
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