169 research outputs found
Uniform sets with few progressions via colorings
Ruzsa asked whether there exist Fourier-uniform subsets of with density and 4-term arithmetic progression (4-APs)
density at most , for arbitrarily large . Gowers constructed
Fourier uniform sets with density and 4-AP density at most
for some small constant . We show that an affirmative
answer to Ruzsa's question would follow from the existence of an
-coloring of without symmetrically colored 4-APs. For a broad
and natural class of constructions of Fourier-uniform subsets of , we show that Ruzsa's question is equivalent to our arithmetic
Ramsey question.
We prove analogous results for all even-length APs. For each odd ,
we show that there exist -uniform subsets of
with density and -AP density at most .
We also prove generalizations to arbitrary one-dimensional patterns.Comment: 20 page
Space-Query Tradeoffs in Range Subgraph Counting and Listing
This paper initializes the study of range subgraph counting and range subgraph listing, both of which are motivated by the significant demands in practice to perform graph analytics on subgraphs pertinent to only selected, as opposed to all, vertices. In the first problem, there is an undirected graph G where each vertex carries a real-valued attribute. Given an interval q and a pattern Q, a query counts the number of occurrences of Q in the subgraph of G induced by the vertices whose attributes fall in q. The second problem has the same setup except that a query needs to enumerate (rather than count) those occurrences with a small delay. In both problems, our goal is to understand the tradeoff between space usage and query cost, or more specifically: (i) given a target on query efficiency, how much pre-computed information about G must we store? (ii) Or conversely, given a budget on space usage, what is the best query time we can hope for? We establish a suite of upper- and lower-bound results on such tradeoffs for various query patterns
Enumerating Subgraphs of Constant Sizes in External Memory
We present an indivisible I/O-efficient algorithm for subgraph enumeration, where the objective is to list all the subgraphs of a massive graph G : = (V, E) that are isomorphic to a pattern graph Q having k = O(1) vertices. Our algorithm performs O((|E|^{k/2})/(M^{{k/2}-1} B) log_{M/B}(|E|/B) + (|E|^?)/(M^{?-1} B) I/Os with high probability, where ? is the fractional edge covering number of Q (it always holds ? ? k/2, regardless of Q), M is the number of words in (internal) memory, and B is the number of words in a disk block. Our solution is optimal in the class of indivisible algorithms for all pattern graphs with ? > k/2. When ? = k/2, our algorithm is still optimal as long as M/B ? (|E|/B)^? for any constant ? > 0
Recurrent Contour-based Instance Segmentation with Progressive Learning
Contour-based instance segmentation has been actively studied, thanks to its
flexibility and elegance in processing visual objects within complex
backgrounds. In this work, we propose a novel deep network architecture, i.e.,
PolySnake, for contour-based instance segmentation. Motivated by the classic
Snake algorithm, the proposed PolySnake achieves superior and robust
segmentation performance with an iterative and progressive contour refinement
strategy. Technically, PolySnake introduces a recurrent update operator to
estimate the object contour iteratively. It maintains a single estimate of the
contour that is progressively deformed toward the object boundary. At each
iteration, PolySnake builds a semantic-rich representation for the current
contour and feeds it to the recurrent operator for further contour adjustment.
Through the iterative refinements, the contour finally progressively converges
to a stable status that tightly encloses the object instance. Moreover, with a
compact design of the recurrent architecture, we ensure the running efficiency
under multiple iterations. Extensive experiments are conducted to validate the
merits of our method, and the results demonstrate that the proposed PolySnake
outperforms the existing contour-based instance segmentation methods on several
prevalent instance segmentation benchmarks. The codes and models are available
at https://github.com/fh2019ustc/PolySnake
Isolation Forest Based Submodule Open-Circuit Fault Localization Method for Modular Multilevel Converters
- …