8,733 research outputs found
Defensive alliances in graphs: a survey
A set of vertices of a graph is a defensive -alliance in if
every vertex of has at least more neighbors inside of than outside.
This is primarily an expository article surveying the principal known results
on defensive alliances in graph. Its seven sections are: Introduction,
Computational complexity and realizability, Defensive -alliance number,
Boundary defensive -alliances, Defensive alliances in Cartesian product
graphs, Partitioning a graph into defensive -alliances, and Defensive
-alliance free sets.Comment: 25 page
Open k-monopolies in graphs: complexity and related concepts
Closed monopolies in graphs have a quite long range of applications in
several problems related to overcoming failures, since they frequently have
some common approaches around the notion of majorities, for instance to
consensus problems, diagnosis problems or voting systems. We introduce here
open -monopolies in graphs which are closely related to different parameters
in graphs. Given a graph and , if is the
number of neighbors has in , is an integer and is a positive
integer, then we establish in this article a connection between the following
three concepts:
- Given a nonempty set a vertex of is said to be
-controlled by if . The set
is called an open -monopoly for if it -controls every vertex of
.
- A function is called a signed total
-dominating function for if for all
.
- A nonempty set is a global (defensive and offensive)
-alliance in if holds for every .
In this article we prove that the problem of computing the minimum
cardinality of an open -monopoly in a graph is NP-complete even restricted
to bipartite or chordal graphs. In addition we present some general bounds for
the minimum cardinality of open -monopolies and we derive some exact values.Comment: 18 pages, Discrete Mathematics & Theoretical Computer Science (2016
A Survey on Alliances and Related Parameters in Graphs
In this paper, we show that several graph parameters are known in different areas under completely different names.More specifically, our observations connect signed domination, monopolies, -domination, -independence,positive influence domination,and a parameter associated to fast information propagationin networks to parameters related to various notions of global -alliances in graphs.We also propose a new framework, called (global) -alliances, not only in order to characterizevarious known variants of alliance and domination parameters, but also to suggest a unifying framework for the study of alliances and domination.Finally, we also give a survey on the mentioned graph parameters, indicating how results transfer due to our observations
Powerful alliances in graphs
AbstractFor a graph G=(V,E), a non-empty set S⊆V is a defensive alliance if for every vertex v in S, v has at most one more neighbor in V−S than it has in S, and S is an offensive alliance if for every v∈V−S that has a neighbor in S, v has more neighbors in S than in V−S. A powerful alliance is both defensive and offensive. We initiate the study of powerful alliances in graphs
Dynamics of alliance formation and the egalitarian revolution
Arguably the most influential force in human history is the formation of
social coalitions and alliances (i.e., long-lasting coalitions) and their
impact on individual power. In most great ape species, coalitions occur at
individual and group levels and among both kin and non-kin. Nonetheless, ape
societies remain essentially hierarchical, and coalitions rarely weaken social
inequality. In contrast, human hunter-gatherers show a remarkable tendency to
egalitarianism, and human coalitions and alliances occur not only among
individuals and groups, but also among groups of groups. Here, we develop a
stochastic model describing the emergence of networks of allies resulting from
within-group competition for status or mates between individuals utilizing
dyadic information. The model shows that alliances often emerge in a phase
transition-like fashion if the group size, awareness, aggressiveness, and
persuasiveness of individuals are large and the decay rate of individual
affinities is small. With cultural inheritance of social networks, a single
leveling alliance including all group members can emerge in several
generations. Our results suggest that a rapid transition from a hierarchical
society of great apes to an egalitarian society of hunter-gatherers (often
referred to as "egalitarian revolution") could indeed follow an increase in
human cognitive abilities. The establishment of stable group-wide egalitarian
alliances creates conditions promoting the origin of cultural norms favoring
the group interests over those of individuals.Comment: 37 pages, 15 figure
Spontaneous centralization of control in a network of company ownerships
We introduce a model for the adaptive evolution of a network of company
ownerships. In a recent work it has been shown that the empirical global
network of corporate control is marked by a central, tightly connected "core"
made of a small number of large companies which control a significant part of
the global economy. Here we show how a simple, adaptive "rich get richer"
dynamics can account for this characteristic, which incorporates the increased
buying power of more influential companies, and in turn results in even higher
control. We conclude that this kind of centralized structure can emerge without
it being an explicit goal of these companies, or as a result of a
well-organized strategy.Comment: 5 Pages, 7 figure
Boundaryless Management - Creating, transforming and using knowledge in inter-organizational collaboration. A literature review
Current literature on organizations often argues that firms are becoming increasingly dependent on knowledge residing outside their own boundaries requiring organizations to increase their entrepreneurial abilities and make their boundaries more flexible and permeable. This paper reviews the literature on what might be called interorganizational knowledge work. Implied in this focus is an assumption of clear organizaitonal boundaries. Rather than taking these boundaries and their importance for granted, the current review, however, aims at relativizing these boundaries. By focusing the empirical phenomenon of collaboration between individuals in different organizations, four different streams of literature with different constructions of the organizational boundary and its importance were identified: the literature on learning in alliances and joint ventures, the literature on collaboration in industrial networks, the literature on social networks and communities of practice and finally the literature on geographical clusters and innovation systems. The above four streams of the literature are reviewed with a special focus on the following three questions: 1. What is the role of (organizational) boundaries in interorganizational knowledge work? 2. What do we know about how these boundaries can be overcome? 3. What are the implications for managing interorganizational knowledge work spelled out in the literature?Interorganizational collaboration; Knowledge Management; Literature review
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