Some results on triangle partitions

We show that there exist efficient algorithms for the triangle packing problem in colored permutation graphs, complete multipartite graphs, distance-hereditary graphs, k-modular permutation graphs and complements of k-partite graphs (when k is fixed). We show that there is an efficient algorithm for C_4-packing on bipartite permutation graphs and we show that C_4-packing on bipartite graphs is NP-complete. We characterize the cobipartite graphs that have a triangle partition

Rebuilding convex sets in graphs

The usual distance between pairs of vertices in a graph naturally gives rise to the notion of an interval between a pair of vertices in a graph. This in turn allows us to extend the notions of convex sets, convex hull, and extreme points in Euclidean space to the vertex set of a graph. The extreme vertices of a graph are known to be precisely the simplicial vertices, i.e., the vertices whose neighborhoods are complete graphs. It is known that the class of graphs with the Minkowski–Krein–Milman property, i.e., the property that every convex set is the convex hull of its extreme points, is precisely the class of chordal graphs without induced 3-fans. We define a vertex to be a contour vertex if the eccentricity of every neighbor is at most as large as that of the vertex. In this paper we show that every convex set of vertices in a graph is the convex hull of the collection of its contour vertices. We characterize those graphs for which every convex set has the property that its contour vertices coincide with its extreme points. A set of vertices in a graph is a geodetic set if the union of the intervals between pairs of vertices in the set, taken over all pairs in the set, is the entire vertex set. We show that the contour vertices in distance hereditary graphs form a geodetic set

Complex event types for agent-based simulation

This thesis presents a novel formal modelling language, complex event types (CETs), to describe behaviours in agent-based simulations. CETs are able to describe behaviours at any computationally represented level of abstraction. Behaviours can be specified both in terms of the state transition rules of the agent-based model that generate them and in terms of the state transition structures themselves. Based on CETs, novel computational statistical methods are introduced which allow statistical dependencies between behaviours at different levels to be established. Different dependencies formalise different probabilistic causal relations and Complex Systems constructs such as ‘emergence’ and ‘autopoiesis’. Explicit links are also made between the different types of CET inter-dependency and the theoretical assumptions they represent. With the novel computational statistical methods, three categories of model can be validated and discovered: (i) inter-level models, which define probabilistic dependencies between behaviours at different levels; (ii) multi-level models, which define the set of simulations for which an inter-level model holds; (iii) inferred predictive models, which define latent relationships between behaviours at different levels. The CET modelling language and computational statistical methods are then applied to a novel agent-based model of Colonic Cancer to demonstrate their applicability to Complex Systems sciences such as Systems Biology. This proof of principle model provides a framework for further development of a detailed integrative model of the system, which can progressively incorporate biological data from different levels and scales as these become available

Youth in Agribusiness in Uganda. An Ethnography of a Development Trend.

Recently, the demographic boom on the African continent, and the consequent challenge of unemployment, has fuelled a focus on ‘youth’. Given that the majority of the African population resides in rural areas, the emphasis of development policies for youth has focused on their employability in the agricultural sector. While the commercialisation of agriculture, as a development theme, has alternated with a focus on food security for decades, the emphasis on youth in agribusiness has come to dominate development policy making and budgeting in the past five years (with country-specific variations). The main research question of this dissertation is: How has the social category of youth been driving a new trend in development around agribusiness, and what has been its impact so far? This study attempts to answer this question for the case of Uganda. Reflecting the demographic trends on the African continent, Uganda has an exceptionally young population, which is mostly employed in agriculture. Like in other countries throughout Africa, over the past few years, increasing attention and budgets have been placed on engaging youths in agribusiness. While unique in many ways, Uganda is a ‘typical case study’ both as an aid recipient and as a participant in the development trend focusing on youth in agribusiness. I studied the emergence of the development trend on youth in agribusiness from two angles: conducting ethnographic research with both development practitioners engaged in the field of agribusiness, and youths working both inside and outside of development schemes. In total, I interviewed 24 representatives of development agencies and 110 youths living in four regions of the country. I also engaged in participant observation, joining development practitioners for field visits, sitting in high-level meetings, and interacting with youths during their agribusiness activities at the markets, in the agricultural fields and visiting their households