6 research outputs found
Multicolored Dynamos on Toroidal Meshes
Detecting on a graph the presence of the minimum number of nodes (target set)
that will be able to "activate" a prescribed number of vertices in the graph is
called the target set selection problem (TSS) proposed by Kempe, Kleinberg, and
Tardos. In TSS's settings, nodes have two possible states (active or
non-active) and the threshold triggering the activation of a node is given by
the number of its active neighbors. Dealing with fault tolerance in a majority
based system the two possible states are used to denote faulty or non-faulty
nodes, and the threshold is given by the state of the majority of neighbors.
Here, the major effort was in determining the distribution of initial faults
leading the entire system to a faulty behavior. Such an activation pattern,
also known as dynamic monopoly (or shortly dynamo), was introduced by Peleg in
1996. In this paper we extend the TSS problem's settings by representing nodes'
states with a "multicolored" set. The extended version of the problem can be
described as follows: let G be a simple connected graph where every node is
assigned a color from a finite ordered set C = {1, . . ., k} of colors. At each
local time step, each node can recolor itself, depending on the local
configurations, with the color held by the majority of its neighbors. Given G,
we study the initial distributions of colors leading the system to a k
monochromatic configuration in toroidal meshes, focusing on the minimum number
of initial k-colored nodes. We find upper and lower bounds to the size of a
dynamo, and then special classes of dynamos, outlined by means of a new
approach based on recoloring patterns, are characterized
Dynamic Monopolies in Colored Tori
The {\em information diffusion} has been modeled as the spread of an
information within a group through a process of social influence, where the
diffusion is driven by the so called {\em influential network}. Such a process,
which has been intensively studied under the name of {\em viral marketing}, has
the goal to select an initial good set of individuals that will promote a new
idea (or message) by spreading the "rumor" within the entire social network
through the word-of-mouth. Several studies used the {\em linear threshold
model} where the group is represented by a graph, nodes have two possible
states (active, non-active), and the threshold triggering the adoption
(activation) of a new idea to a node is given by the number of the active
neighbors.
The problem of detecting in a graph the presence of the minimal number of
nodes that will be able to activate the entire network is called {\em target
set selection} (TSS). In this paper we extend TSS by allowing nodes to have
more than two colors. The multicolored version of the TSS can be described as
follows: let be a torus where every node is assigned a color from a finite
set of colors. At each local time step, each node can recolor itself, depending
on the local configurations, with the color held by the majority of its
neighbors. We study the initial distributions of colors leading the system to a
monochromatic configuration of color , focusing on the minimum number of
initial -colored nodes. We conclude the paper by providing the time
complexity to achieve the monochromatic configuration
Rooting opinions in the minds: a cognitive model and a formal account of opinions and their dynamics
The study of opinions, their formation and change, is one of the defining
topics addressed by social psychology, but in recent years other disciplines,
like computer science and complexity, have tried to deal with this issue.
Despite the flourishing of different models and theories in both fields,
several key questions still remain unanswered. The understanding of how
opinions change and the way they are affected by social influence are
challenging issues requiring a thorough analysis of opinion per se but also of
the way in which they travel between agents' minds and are modulated by these
exchanges. To account for the two-faceted nature of opinions, which are mental
entities undergoing complex social processes, we outline a preliminary model in
which a cognitive theory of opinions is put forward and it is paired with a
formal description of them and of their spreading among minds. Furthermore,
investigating social influence also implies the necessity to account for the
way in which people change their minds, as a consequence of interacting with
other people, and the need to explain the higher or lower persistence of such
changes
Understanding opinions. A cognitive and formal account
The study of opinions, their formation and change, is one of the defining
topics addressed by social psychology, but in recent years other disciplines,
as computer science and complexity, have addressed this challenge. Despite the
flourishing of different models and theories in both fields, several key
questions still remain unanswered. The aim of this paper is to challenge the
current theories on opinion by putting forward a cognitively grounded model
where opinions are described as specific mental representations whose main
properties are put forward. A comparison with reputation will be also
presented
Opinions within Media, Power and Gossip
Despite the increasing diffusion of the Internet technology, TV remains the
principal medium of communication. People's perceptions, knowledge, beliefs and
opinions about matter of facts get (in)formed through the information reported
on by the mass-media. However, a single source of information (and consensus)
could be a potential cause of anomalies in the structure and evolution of a
society. Hence, as the information available (and the way it is reported) is
fundamental for our perceptions and opinions, the definition of conditions
allowing for a good information to be disseminated is a pressing challenge. In
this paper starting from a report on the last Italian political campaign in
2008, we derive a socio-cognitive computational model of opinion dynamics where
agents get informed by different sources of information. Then, a what-if
analysis, performed trough simulations on the model's parameters space, is
shown. In particular, the scenario implemented includes three main streams of
information acquisition, differing in both the contents and the perceived
reliability of the messages spread. Agents' internal opinion is updated either
by accessing one of the information sources, namely media and experts, or by
exchanging information with one another. They are also endowed with cognitive
mechanisms to accept, reject or partially consider the acquired information