71 research outputs found
The Four Bars Problem
A four-bar linkage is a mechanism consisting of four rigid bars which are
joined by their endpoints in a polygonal chain and which can rotate freely at
the joints (or vertices). We assume that the linkage lies in the 2-dimensional
plane so that one of the bars is held horizontally fixed. In this paper we
consider the problem of reconfiguring a four-bar linkage using an operation
called a \emph{pop}. Given a polygonal cycle, a pop reflects a vertex across
the line defined by its two adjacent vertices along the polygonal chain. Our
main result shows that for certain conditions on the lengths of the bars of the
four-bar linkage, the neighborhood of any configuration that can be reached by
smooth motion can also be reached by pops. The proof relies on the fact that
pops are described by a map on the circle with an irrational number of
rotation.Comment: 18 page
Orderly broadcasting in multidimensional tori
In this thesis, we describe an ordering of the vertices of a multidimensional torus and study the upper bound on the orderly broadcast time. Along with messy broadcasting, orderly broadcasting is another model where the nodes of the network have limited knowledge about their local neighborhood. However, while messy broadcasting explores the worst-case performance of broadcast schemes, orderly broadcasting, like the classical broadcast model, is concerned with finding an ordering of the vertices of a graph that will minimize the overall broadcast time
Efficient Multi-Robot Coverage of a Known Environment
This paper addresses the complete area coverage problem of a known
environment by multiple-robots. Complete area coverage is the problem of moving
an end-effector over all available space while avoiding existing obstacles. In
such tasks, using multiple robots can increase the efficiency of the area
coverage in terms of minimizing the operational time and increase the
robustness in the face of robot attrition. Unfortunately, the problem of
finding an optimal solution for such an area coverage problem with multiple
robots is known to be NP-complete. In this paper we present two approximation
heuristics for solving the multi-robot coverage problem. The first solution
presented is a direct extension of an efficient single robot area coverage
algorithm, based on an exact cellular decomposition. The second algorithm is a
greedy approach that divides the area into equal regions and applies an
efficient single-robot coverage algorithm to each region. We present
experimental results for two algorithms. Results indicate that our approaches
provide good coverage distribution between robots and minimize the workload per
robot, meanwhile ensuring complete coverage of the area.Comment: In proceedings of IEEE/RSJ International Conference on Intelligent
Robots and Systems (IROS), 201
OC-NMN: Object-centric Compositional Neural Module Network for Generative Visual Analogical Reasoning
A key aspect of human intelligence is the ability to imagine -- composing
learned concepts in novel ways -- to make sense of new scenarios. Such capacity
is not yet attained for machine learning systems. In this work, in the context
of visual reasoning, we show how modularity can be leveraged to derive a
compositional data augmentation framework inspired by imagination. Our method,
denoted Object-centric Compositional Neural Module Network (OC-NMN), decomposes
visual generative reasoning tasks into a series of primitives applied to
objects without using a domain-specific language. We show that our modular
architectural choices can be used to generate new training tasks that lead to
better out-of-distribution generalization. We compare our model to existing and
new baselines in proposed visual reasoning benchmark that consists of applying
arithmetic operations to MNIST digits
Theta-3 is connected
In this paper, we show that the -graph with three cones is connected.
We also provide an alternative proof of the connectivity of the Yao graph with
three cones.Comment: 11 pages, to appear in CGT
Using Graph Algorithms to Pretrain Graph Completion Transformers
Recent work on Graph Neural Networks has demonstrated that self-supervised
pretraining can further enhance performance on downstream graph, link, and node
classification tasks. However, the efficacy of pretraining tasks has not been
fully investigated for downstream large knowledge graph completion tasks. Using
a contextualized knowledge graph embedding approach, we investigate five
different pretraining signals, constructed using several graph algorithms and
no external data, as well as their combination. We leverage the versatility of
our Transformer-based model to explore graph structure generation pretraining
tasks (i.e. path and k-hop neighborhood generation), typically inapplicable to
most graph embedding methods. We further propose a new path-finding algorithm
guided by information gain and find that it is the best-performing pretraining
task across three downstream knowledge graph completion datasets. While using
our new path-finding algorithm as a pretraining signal provides 2-3% MRR
improvements, we show that pretraining on all signals together gives the best
knowledge graph completion results. In a multitask setting that combines all
pretraining tasks, our method surpasses the latest and strong performing
knowledge graph embedding methods on all metrics for FB15K-237, on MRR and
Hit@1 for WN18RRand on MRR and hit@10 for JF17K (a knowledge hypergraph
dataset)
The Distance Geometry of Music
We demonstrate relationships between the classic Euclidean algorithm and many
other fields of study, particularly in the context of music and distance
geometry. Specifically, we show how the structure of the Euclidean algorithm
defines a family of rhythms which encompass over forty timelines
(\emph{ostinatos}) from traditional world music. We prove that these
\emph{Euclidean rhythms} have the mathematical property that their onset
patterns are distributed as evenly as possible: they maximize the sum of the
Euclidean distances between all pairs of onsets, viewing onsets as points on a
circle. Indeed, Euclidean rhythms are the unique rhythms that maximize this
notion of \emph{evenness}. We also show that essentially all Euclidean rhythms
are \emph{deep}: each distinct distance between onsets occurs with a unique
multiplicity, and these multiplicies form an interval . Finally,
we characterize all deep rhythms, showing that they form a subclass of
generated rhythms, which in turn proves a useful property called shelling. All
of our results for musical rhythms apply equally well to musical scales. In
addition, many of the problems we explore are interesting in their own right as
distance geometry problems on the circle; some of the same problems were
explored by Erd\H{o}s in the plane.Comment: This is the full version of the paper: "The distance geometry of deep
rhythms and scales." 17th Canadian Conference on Computational Geometry (CCCG
'05), University of Windsor, Canada, 200
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