17,815 research outputs found
On Exact Algorithms for Permutation CSP
In the Permutation Constraint Satisfaction Problem (Permutation CSP) we are
given a set of variables and a set of constraints C, in which constraints
are tuples of elements of V. The goal is to find a total ordering of the
variables, , which satisfies as many
constraints as possible. A constraint is satisfied by an
ordering when . An instance has arity
if all the constraints involve at most elements.
This problem expresses a variety of permutation problems including {\sc
Feedback Arc Set} and {\sc Betweenness} problems. A naive algorithm, listing
all the permutations, requires time. Interestingly, {\sc
Permutation CSP} for arity 2 or 3 can be solved by Held-Karp type algorithms in
time , but no algorithm is known for arity at least 4 with running
time significantly better than . In this paper we resolve the
gap by showing that {\sc Arity 4 Permutation CSP} cannot be solved in time
unless ETH fails
Improved Parameterized Algorithms for Constraint Satisfaction
For many constraint satisfaction problems, the algorithm which chooses a
random assignment achieves the best possible approximation ratio. For instance,
a simple random assignment for {\sc Max-E3-Sat} allows 7/8-approximation and
for every \eps >0 there is no polynomial-time (7/8+\eps)-approximation
unless P=NP. Another example is the {\sc Permutation CSP} of bounded arity.
Given the expected fraction of the constraints satisfied by a random
assignment (i.e. permutation), there is no (\rho+\eps)-approximation
algorithm for every \eps >0, assuming the Unique Games Conjecture (UGC).
In this work, we consider the following parameterization of constraint
satisfaction problems. Given a set of constraints of constant arity, can we
satisfy at least constraint, where is the expected fraction
of constraints satisfied by a random assignment? {\sc Constraint Satisfaction
Problems above Average} have been posed in different forms in the literature
\cite{Niedermeier2006,MahajanRamanSikdar09}. We present a faster parameterized
algorithm for deciding whether equations can be simultaneously
satisfied over . As a consequence, we obtain -variable
bikernels for {\sc boolean CSPs} of arity for every fixed , and for {\sc
permutation CSPs} of arity 3. This implies linear bikernels for many problems
under the "above average" parameterization, such as {\sc Max--Sat}, {\sc
Set-Splitting}, {\sc Betweenness} and {\sc Max Acyclic Subgraph}. As a result,
all the parameterized problems we consider in this paper admit -time
algorithms.
We also obtain non-trivial hybrid algorithms for every Max -CSP: for every
instance , we can either approximate beyond the random assignment
threshold in polynomial time, or we can find an optimal solution to in
subexponential time.Comment: A preliminary version of this paper has been accepted for IPEC 201
Brain Control of Movement Execution Onset Using Local Field Potentials in Posterior Parietal Cortex
The precise control of movement execution onset is essential for safe and autonomous cortical motor prosthetics. A recent study from the parietal reach region (PRR) suggested that the local field potentials (LFPs) in this area might be useful for decoding execution time information because of the striking difference in the LFP spectrum between the plan and execution states (Scherberger et al., 2005). More specifically, the LFP power in the 0–10 Hz band sharply rises while the power in the 20–40 Hz band falls as the state transitions from plan to execution. However, a change of visual stimulus immediately preceded reach onset, raising the possibility that the observed spectral change reflected the visual event instead of the reach onset. Here, we tested this possibility and found that the LFP spectrum change was still time locked to the movement onset in the absence of a visual event in self-paced reaches. Furthermore, we successfully trained the macaque subjects to use the LFP spectrum change as a "go" signal in a closed-loop brain-control task in which the animals only modulated the LFP and did not execute a reach. The execution onset was signaled by the change in the LFP spectrum while the target position of the cursor was controlled by the spike firing rates recorded from the same site. The results corroborate that the LFP spectrum change in PRR is a robust indicator for the movement onset and can be used for control of execution onset in a cortical prosthesis
A polynomial kernel for Block Graph Deletion
In the Block Graph Deletion problem, we are given a graph on vertices
and a positive integer , and the objective is to check whether it is
possible to delete at most vertices from to make it a block graph,
i.e., a graph in which each block is a clique. In this paper, we obtain a
kernel with vertices for the Block Graph Deletion problem.
This is a first step to investigate polynomial kernels for deletion problems
into non-trivial classes of graphs of bounded rank-width, but unbounded
tree-width. Our result also implies that Chordal Vertex Deletion admits a
polynomial-size kernel on diamond-free graphs. For the kernelization and its
analysis, we introduce the notion of `complete degree' of a vertex. We believe
that the underlying idea can be potentially applied to other problems. We also
prove that the Block Graph Deletion problem can be solved in time .Comment: 22 pages, 2 figures, An extended abstract appeared in IPEC201
Does Postsecondary Education Attainment Matter in Community Service Engagement? Evidence from Across 18 OECD Countries
This study is concerned with the central issues of community service engagement (CSE) in 21st century democratic societies around the world. To examine the factors influencing postsecondary education attainment’s relationship to CSE, this study utilized data from the Organization for Economic Co-operation and Development (OECD) countries using ordinary least square (OLS) and two-level hierarchical linear modeling (HLM) methods, including various factors for each country’s individual and country levels. The results show that attainment in postsecondary education at the individual level and investment and enrollments in tertiary education both have an influence on increasing CSE in 18 OECD countries. The present study is expected to contribute to an understanding of the relationship between postsecondary education and CSE across the world
Smart Engagement and Smart Urbanism: Integrating "The Smart" Into Participatory Planning and Community Engagement
The smart city epitomizes a new paradigm shift in urban planning, policy, and cities. Smart cities require and are powered by smart city principles to succeed, including smart technologies, smart infrastructure, and smart governance; however, they also need to engage closely with the citizens who are most affected by the deployment of the smart city and who also embrace the diverse perspectives, experiences, and opportunities of living in smart cities, i.e., smart engagement. What would be forms of collaborative democracy and inclusive citizen participation in smart city planning? To what extent can smart city planning respond and address inequality, justice, and social and digital division? How can we create community-based climate change planning with the smart? What would be a smart community platform that supports smart engagement, and how do cities around the world establish smart city policy and assess the impact on smart engagement? This thematic issue aims to answer these questions by exploring new visions, facets and methods, practices, and tools for enabling smart engagement. Drawing on research from various countries and cities across the world, the contributions bring new prospects of smart engagement and smart urbanism and illuminate how the theory, plan and policy, and practices of smart engagements are binding to the extent of citizen participation and engagement in smart cities
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