332 research outputs found
Asymmetric coloring games on incomparability graphs
Consider the following game on a graph : Alice and Bob take turns coloring
the vertices of properly from a fixed set of colors; Alice wins when the
entire graph has been colored, while Bob wins when some uncolored vertices have
been left. The game chromatic number of is the minimum number of colors
that allows Alice to win the game. The game Grundy number of is defined
similarly except that the players color the vertices according to the first-fit
rule and they only decide on the order in which it is applied. The -game
chromatic and Grundy numbers are defined likewise except that Alice colors
vertices and Bob colors vertices in each round. We study the behavior of
these parameters for incomparability graphs of posets with bounded width. We
conjecture a complete characterization of the pairs for which the
-game chromatic and Grundy numbers are bounded in terms of the width of
the poset; we prove that it gives a necessary condition and provide some
evidence for its sufficiency. We also show that the game chromatic number is
not bounded in terms of the Grundy number, which answers a question of Havet
and Zhu
Coloring triangle-free rectangle overlap graphs with colors
Recently, it was proved that triangle-free intersection graphs of line
segments in the plane can have chromatic number as large as . Essentially the same construction produces -chromatic
triangle-free intersection graphs of a variety of other geometric
shapes---those belonging to any class of compact arc-connected sets in
closed under horizontal scaling, vertical scaling, and
translation, except for axis-parallel rectangles. We show that this
construction is asymptotically optimal for intersection graphs of boundaries of
axis-parallel rectangles, which can be alternatively described as overlap
graphs of axis-parallel rectangles. That is, we prove that triangle-free
rectangle overlap graphs have chromatic number , improving on
the previous bound of . To this end, we exploit a relationship
between off-line coloring of rectangle overlap graphs and on-line coloring of
interval overlap graphs. Our coloring method decomposes the graph into a
bounded number of subgraphs with a tree-like structure that "encodes"
strategies of the adversary in the on-line coloring problem. Then, these
subgraphs are colored with colors using a combination of
techniques from on-line algorithms (first-fit) and data structure design
(heavy-light decomposition).Comment: Minor revisio
Miłosz i Andrzejewski — trudny dialog
The article brings an attempt at a reconstruction of a dialogue of both writers on the basis of correspondence and literary works. In spite of the author’s introductory remarks, correspondence documents were used to a minimal degree, whereas more attention was paid to the image of Andrzejewski in The Captive Mind, ideological evolution of the Ashes and diamonds author’s as well as his biography.The article brings an attempt at a reconstruction of a dialogue of both writers on the basis of correspondence and literary works. In spite of the author’s introductory remarks, correspondence documents were used to a minimal degree, whereas more attention was paid to the image of Andrzejewski in The Captive Mind, ideological evolution of the Ashes and diamonds author’s as well as his biography
A survey on learning from imbalanced data streams: taxonomy, challenges, empirical study, and reproducible experimental framework
Class imbalance poses new challenges when it comes to classifying data
streams. Many algorithms recently proposed in the literature tackle this
problem using a variety of data-level, algorithm-level, and ensemble
approaches. However, there is a lack of standardized and agreed-upon procedures
on how to evaluate these algorithms. This work presents a taxonomy of
algorithms for imbalanced data streams and proposes a standardized, exhaustive,
and informative experimental testbed to evaluate algorithms in a collection of
diverse and challenging imbalanced data stream scenarios. The experimental
study evaluates 24 state-of-the-art data streams algorithms on 515 imbalanced
data streams that combine static and dynamic class imbalance ratios,
instance-level difficulties, concept drift, real-world and semi-synthetic
datasets in binary and multi-class scenarios. This leads to the largest
experimental study conducted so far in the data stream mining domain. We
discuss the advantages and disadvantages of state-of-the-art classifiers in
each of these scenarios and we provide general recommendations to end-users for
selecting the best algorithms for imbalanced data streams. Additionally, we
formulate open challenges and future directions for this domain. Our
experimental testbed is fully reproducible and easy to extend with new methods.
This way we propose the first standardized approach to conducting experiments
in imbalanced data streams that can be used by other researchers to create
trustworthy and fair evaluation of newly proposed methods. Our experimental
framework can be downloaded from
https://github.com/canoalberto/imbalanced-streams
Where Have the Litigants Gone?
The recognition of coral species based on underwater texture images pose a
significant difficulty for machine learning algorithms, due to the three
following challenges embedded in the nature of this data: 1) datasets do not
include information about the global structure of the coral; 2) several species
of coral have very similar characteristics; and 3) defining the spatial borders
between classes is difficult as many corals tend to appear together in groups.
For this reason, the classification of coral species has always required an aid
from a domain expert. The objective of this paper is to develop an accurate
classification model for coral texture images. Current datasets contain a large
number of imbalanced classes, while the images are subject to inter-class
variation. We have analyzed 1) several Convolutional Neural Network (CNN)
architectures, 2) data augmentation techniques and 3) transfer learning. We
have achieved the state-of-the art accuracies using different variations of
ResNet on the two current coral texture datasets, EILAT and RSMAS.Comment: 22 pages, 10 figure
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