458 research outputs found
Low power general purpose loop acceleration for NDP applications
Modern processor architectures face a throughput scaling problem as the performance bottleneck shifts from the core pipeline to the data transfer operations between the dynamic random access memory (DRAM) and the processor chip. To address such issue researchers have proposed the near-data processing (NDP) paradigm in which the instruction execution is moved to the DRAM die thus, lowering the data movement between the processor and the DRAM. Previous NDP works focus on specific application types and thus the general purpose application execution paradigm is neglected. In this work we propose an NDP methodology for low power general purpose loop acceleration. For this reason we design and implement a hardware loop accelerator from the ground up to improve the throughput and lower the power consumption of general purpose loops. We adopt a novel loop scheduling approach which enables the loop accelerator to take advantage of the dataflow parallelism of the executing loop and we implement our design on the logic layer of a hybrid memory cube (HMC) DRAM. Post-layout simulations demonstrate an average speedup factor of 20.5x when executing kernels from various scientific fields while the energy consumption is reduced by a factor of 9.3x over the host CPU execution
Neuronal networks in the developing brain are adversely modulated by early psychosocial neglect
The brain's neural circuitry plays a ubiquitous role across domains in cognitive processing and undergoes extensive re-organization during the course of development in part as a result of experience. In this paper we investigated the effects of profound early psychosocial neglect associated with institutional rearing on the development of task-independent brain networks, estimated from longitudinally acquired electroencephalographic (EEG) data from <30 to 96 months, in three cohorts of children from the Bucharest Early Intervention Project (BEIP), including abandoned children reared in institutions who were randomly assigned either to a foster care intervention or to remain in care as usual and never institutionalized children. Two aberrantly connected brain networks were identified in children that had been reared in institutions: 1) a hyper-connected parieto-occipital network, which included cortical hubs and connections that may partially overlap with default-mode network and 2) a hypo-connected network between left temporal and distributed bilateral regions, both of which were aberrantly connected across neural oscillations. This study provides the first evidence of the adverse effects of early psychosocial neglect on the wiring of the developing brain. Given these networks' potentially significant role in various cognitive processes, including memory, learning, social communication and language, these findings suggest that institutionalization in early life may profoundly impact the neural correlates underlying multiple cognitive domains, in ways that may not be fully reversible in the short term
An Algorithmic Meta-Theorem for Graph Modification to Planarity and FOL
In general, a graph modification problem is defined by a graph modification
operation and a target graph property . Typically, the
modification operation may be vertex removal}, edge removal}, edge
contraction}, or edge addition and the question is, given a graph and an
integer , whether it is possible to transform to a graph in
after applying times the operation on . This problem has
been extensively studied for particilar instantiations of and
. In this paper we consider the general property
of being planar and, moreover, being a model of some First-Order Logic sentence
(an FOL-sentence). We call the corresponding meta-problem Graph
-Modification to Planarity and and prove the following
algorithmic meta-theorem: there exists a function
such that, for every and every FOL sentence , the Graph
-Modification to Planarity and is solvable in
time. The proof constitutes a hybrid of two different
classic techniques in graph algorithms. The first is the irrelevant vertex
technique that is typically used in the context of Graph Minors and deals with
properties such as planarity or surface-embeddability (that are not
FOL-expressible) and the second is the use of Gaifman's Locality Theorem that
is the theoretical base for the meta-algorithmic study of FOL-expressible
problems
Fixed-Parameter Tractability of Maximum Colored Path and Beyond
We introduce a general method for obtaining fixed-parameter algorithms for
problems about finding paths in undirected graphs, where the length of the path
could be unbounded in the parameter. The first application of our method is as
follows.
We give a randomized algorithm, that given a colored -vertex undirected
graph, vertices and , and an integer , finds an -path
containing at least different colors in time . This is the
first FPT algorithm for this problem, and it generalizes the algorithm of
Bj\"orklund, Husfeldt, and Taslaman [SODA 2012] on finding a path through
specified vertices. It also implies the first time algorithm for
finding an -path of length at least .
Our method yields FPT algorithms for even more general problems. For example,
we consider the problem where the input consists of an -vertex undirected
graph , a matroid whose elements correspond to the vertices of and
which is represented over a finite field of order , a positive integer
weight function on the vertices of , two sets of vertices , and integers , and the task is to find vertex-disjoint paths
from to so that the union of the vertices of these paths contains an
independent set of of cardinality and weight , while minimizing the
sum of the lengths of the paths. We give a
time randomized algorithm for this problem.Comment: 50 pages, 16 figure
Shortest Cycles With Monotone Submodular Costs
We introduce the following submodular generalization of the Shortest Cycle
problem. For a nonnegative monotone submodular cost function defined on the
edges (or the vertices) of an undirected graph , we seek for a cycle in
of minimum cost . We give an algorithm that given an
-vertex graph , parameter , and the function
represented by an oracle, in time finds a
cycle in with . This is in
sharp contrast with the non-approximability of the closely related Monotone
Submodular Shortest -Path problem, which requires exponentially many
queries to the oracle for finding an -approximation [Goel
et al., FOCS 2009]. We complement our algorithm with a matching lower bound. We
show that for every , obtaining a
-approximation requires at least queries to the oracle. When the function is integer-valued,
our algorithm yields that a cycle of cost can be found in time
. In particular, for
this gives a quasipolynomial-time algorithm
computing a cycle of minimum submodular cost. Interestingly, while a
quasipolynomial-time algorithm often serves as a good indication that a
polynomial time complexity could be achieved, we show a lower bound that
queries are required even when .Comment: 17 pages, 1 figure. Accepted to SODA 202
Compound Logics for Modification Problems
We introduce a novel model-theoretic framework inspired from graph
modification and based on the interplay between model theory and algorithmic
graph minors. The core of our framework is a new compound logic operating with
two types of sentences, expressing graph modification: the modulator sentence,
defining some property of the modified part of the graph, and the target
sentence, defining some property of the resulting graph. In our framework,
modulator sentences are in counting monadic second-order logic (CMSOL) and have
models of bounded treewidth, while target sentences express first-order logic
(FOL) properties along with minor-exclusion. Our logic captures problems that
are not definable in first-order logic and, moreover, may have instances of
unbounded treewidth. Also, it permits the modeling of wide families of problems
involving vertex/edge removals, alternative modulator measures (such as
elimination distance or -treewidth), multistage modifications, and
various cut problems. Our main result is that, for this compound logic,
model-checking can be done in quadratic time. All derived algorithms are
constructive and this, as a byproduct, extends the constructibility horizon of
the algorithmic applications of the Graph Minors theorem of Robertson and
Seymour. The proposed logic can be seen as a general framework to capitalize on
the potential of the irrelevant vertex technique. It gives a way to deal with
problem instances of unbounded treewidth, for which Courcelle's theorem does
not apply. The proof of our meta-theorem combines novel combinatorial results
related to the Flat Wall theorem along with elements of the proof of
Courcelle's theorem and Gaifman's theorem. We finally prove extensions where
the target property is expressible in FOL+DP, i.e., the enhancement of FOL with
disjoint-paths predicates
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