The Complexity of Graph Exploration Games

The graph exploration problem asks a searcher to explore an unknown graph. This problem can be interpreted as the online version of the Traveling Salesman Problem. The treasure hunt problem is the corresponding online version of the shortest s-t-path problem. It asks the searcher to find a specific vertex in an unknown graph at which a treasure is hidden. Recently, the analysis of the impact of a priori knowledge is of interest. In graph problems, one form of a priori knowledge is a map of the graph. We survey the graph exploration and treasure hunt problem with an unlabeled map, which is an isomorphic copy of the graph, that is provided to the searcher. We formulate decision variants of both problems by interpreting the online problems as a game between the online algorithm (the searcher) and the adversary. The map, however, is not controllable by the adversary. The question is, whether the searcher is able to explore the graph fully or find the treasure for all possible decisions of the adversary. We prove the PSPACE-completeness of these games, whereby we analyze the variations which ask for the mere existence of a tour through the graph or path to the treasure and the variations that include costs. Additionally, we analyze the complexity of related problems that ask for a tour in the graph or a s-t path

Cultural Diversification and Decimation in the Prehistoric Record

The history of human cultures is frequently marked by a distinctive pattern of evolution that paleobiologists term diversification and decimation. Under this process, fundamentally new socioeconomic systems appear during periods of dramatic cultural diversification, typically through cultural cladogenesis. Significant diversification episodes come about under conditions that favor group economic success under effective or geographic isolation. Typically shortlived, they are often followed by abrupt decimation under more competitive economic conditions. Regional archaeological sequences, viewed from this perspective, suggest that (1) cultural evolutionary trends are strongly conditioned by historical contingency, though general evolutionary processes are continuously active; (2) the emergence of new systems may be contingent on economic opportunities associated with niche reorganization; and (3) severe competition such as that associated with demographic stress will generally favor decimation

From Data to Actions in Intelligent Transportation Systems: A Prescription of Functional Requirements for Model Actionability

Advances in Data Science permeate every field of Transportation Science and Engineering, resulting in developments in the transportation sector that are data-driven. Nowadays, Intelligent Transportation Systems (ITS) could be arguably approached as a “story” intensively producing and consuming large amounts of data. A diversity of sensing devices densely spread over the infrastructure, vehicles or the travelers’ personal devices act as sources of data flows that are eventually fed into software running on automatic devices, actuators or control systems producing, in turn, complex information flows among users, traffic managers, data analysts, traffic modeling scientists, etc. These information flows provide enormous opportunities to improve model development and decision-making. This work aims to describe how data, coming from diverse ITS sources, can be used to learn and adapt data-driven models for efficiently operating ITS assets, systems and processes; in other words, for data-based models to fully become actionable. Grounded in this described data modeling pipeline for ITS, we define the characteristics, engineering requisites and challenges intrinsic to its three compounding stages, namely, data fusion, adaptive learning and model evaluation. We deliberately generalize model learning to be adaptive, since, in the core of our paper is the firm conviction that most learners will have to adapt to the ever-changing phenomenon scenario underlying the majority of ITS applications. Finally, we provide a prospect of current research lines within Data Science that can bring notable advances to data-based ITS modeling, which will eventually bridge the gap towards the practicality and actionability of such models.This work was supported in part by the Basque Government for its funding support through the EMAITEK program (3KIA, ref. KK-2020/00049). It has also received funding support from the Consolidated Research Group MATHMODE (IT1294-19) granted by the Department of Education of the Basque Government

ℓ-CTP: Utilizing Multiple Agents to Find Efficient Routes in Disrupted Networks

Recent hurricane seasons have demonstrated the need for more effective methods of coping with flooding of roadways. A key complaint of logistics managers is the lack of knowledge when developing routes for vehicles attempting to navigate through areas which may be flooded. In particular, it can be difficult to re-route large vehicles upon encountering a flooded roadway. We utilize the Canadian Traveller’s Problem (CTP) to construct an online framework for utilizing multiple vehicles to discover low-cost paths through networks with failed edges unknown to one or more agents a priori. This thesis demonstrates the following results: first, we develop the ℓ-CTP framework to extend a theoretically validated set of path planning policies for a single agent in combination with the iterative penalty method, which incentivizes a group of ℓ \u3e 1 agents to explore dissimilar paths on a graph between a common origin and destination. Second, we carry out simulations on random graphs to determine the impact of the addition of agents on the path cost found. Through statistical analysis of graphs of multiple sizes, we validate our technique against prior work and demonstrate that path cost can be modeled as an exponential decay function on the number of agents. Finally, we demonstrate that our approach can scale to large graphs, and the results found on random graphs hold for a simulation of the Houston metro area during hurricane Harvey

Problèmes de tournées multicritères dans des graphes

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal