Majority Opinion Diffusion in Social Networks: An Adversarial Approach

We introduce and study a novel majority-based opinion diffusion model. Consider a graph $G$, which represents a social network. Assume that initially a subset of nodes, called seed nodes or early adopters, are colored either black or white, which correspond to positive or negative opinion regarding a consumer product or a technological innovation. Then, in each round an uncolored node, which is adjacent to at least one colored node, chooses the most frequent color among its neighbors. Consider a marketing campaign which advertises a product of poor quality and its ultimate goal is that more than half of the population believe in the quality of the product at the end of the opinion diffusion process. We focus on three types of attackers which can select the seed nodes in a deterministic or random fashion and manipulate almost half of them to adopt a positive opinion toward the product (that is, to choose black color). We say that an attacker succeeds if a majority of nodes are black at the end of the process. Our main purpose is to characterize classes of graphs where an attacker cannot succeed. In particular, we prove that if the maximum degree of the underlying graph is not too large or if it has strong expansion properties, then it is fairly resilient to such attacks. Furthermore, we prove tight bounds on the stabilization time of the process (that is, the number of rounds it needs to end) in both settings of choosing the seed nodes deterministically and randomly. We also provide several hardness results for some optimization problems regarding stabilization time and choice of seed nodes.Comment: To appear in AAAI 202

Quick Trips: On the Oriented Diameter of Graphs

In this dissertation, I will discuss two results on the oriented diameter of graphs with certain properties. In the first problem, I studied the oriented diameter of a graph G. Erdos et al. in 1989 showed that for any graph with |V | = n and δ(G) = δ the maximum the diameter could possibly be was 3 n/ δ+1. I considered whether there exists an orientation on a given graph with |G| = n and δ(G) = δ that has a small diameter. Bau and Dankelmann (2015) showed that there is an orientation of diameter 11 n/ δ+1 + O(1), and showed that there is a graph which the best orientation admitted is 3 n/ δ+1 + O(1). It was left as an open question whether the factor of 11 in the first result could be reduced to 3. The result above was improved to 7 n / δ+1 +O(1) by Surmacs (2017) and I will present a proof of a further improvement of this bound to 5 n/δ−1 + O(1). It remains open whether 3 is the best answer. In the second problem, I studied the oriented diameter of the complete graph Kn with some edges removed. We will show that given Kn with n \u3e= 5 and any collection of edges Ev, with |Ev| = n − 5, that there is an orientation of this graph with diameter 2. It remains a question how many edges we can remove to guarantee larger diameters