8 research outputs found
Bears with Hats and Independence Polynomials
Consider the following hat guessing game. A bear sits on each vertex of a
graph , and a demon puts on each bear a hat colored by one of colors.
Each bear sees only the hat colors of his neighbors. Based on this information
only, each bear has to guess colors and he guesses correctly if his hat
color is included in his guesses. The bears win if at least one bear guesses
correctly for any hat arrangement.
We introduce a new parameter - fractional hat chromatic number ,
arising from the hat guessing game. The parameter is related to the
hat chromatic number which has been studied before. We present a surprising
connection between the hat guessing game and the independence polynomial of
graphs. This connection allows us to compute the fractional hat chromatic
number of chordal graphs in polynomial time, to bound fractional hat chromatic
number by a function of maximum degree of , and to compute the exact value
of of cliques, paths, and cycles
Online Ramsey numbers: Long versus short cycles
Online Ramsey game is played between Builder and Painter on an infinite board
. In every round Builder selects an edge, then Painter colors it
red or blue. Both know target graphs and . Builder aims to create
either a red copy of or a blue copy of in as soon
as possible, and Painter tries to prevent it. The online Ramsey number
is the minimum number of rounds such that the Builder
wins. We study where is fixed and is large. We
show that for an absolute constant if
is even, while if is odd
Controlling the Spread of Two Secrets in Diverse Social Networks (Student Abstract)
Information diffusion in social networks is a well-studied concept in social choice theory. We propose the study of the diffusion of two secrets in a heterogeneous environment from the complexity perspective, that is, there are two different networks with the same set of agents (e.g., the structure of the set of followers might be different in two distinct social networks).
Formally, our model combines two group identification processes for which we do have independent desiderata---either constructive, where we would like a given group of agents to be exposed to a secret, or destructive, where a given group of agents should not be exposed to a secret. To be able to reach these targets, we can either delete an agent or introduce a previously latent agent.
Our results are mostly negative---all of the problems are NP-hard. Therefore, we propose a parameterized study with respect to the natural parameters, the number of influenced agents, the size of the required/protected agent sets, and the duration of the diffusion process. Most of the studied problems remain W[1]-hard even for a combination of these parameters. We complement these results with nearly optimal XP algorithms
The Parameterized Complexity of Network Microaggregation
Microaggregation is a classical statistical disclosure control technique which requires the input data to be partitioned into clusters while adhering to specified size constraints. We provide novel exact algorithms and lower bounds for the task of microaggregating a given network while considering both unrestricted and connected clusterings, and analyze these from the perspective of the parameterized complexity paradigm. Altogether, our results assemble a complete complexity-theoretic picture for the network microaggregation problem with respect to the most natural parameterizations of the problem, including input-specified parameters capturing the size and homogeneity of the clusters as well as the treewidth and vertex cover number of the network