Now showing 1 - 8 of 8
  • Publication
    Modelling fairness in Food Value Chains: Developing quantitative indicators
    To provide tools and approaches to enable decision makers in food value chains to evaluate the impact of strategic and operational policies aimed at enhancing fairness, integrity, resilience in future scenarios of sustainable food value chains (FVCs). Fairness in food value chains (FVCs) is topical and policy-relevant. Thus there is value in exploring its dynamics through simulation modeling.
  • Publication
    Ethnography in and around an Algorithm
    If 'headwork' is "the conceptual work that informs ethnographic fieldwork and its various representational practices", then this paper is a piece of headwork about what an ethnography in (or around, or of) an algorithm might entail. We begin by situating this question in ethnography’s long tradition of philosophical reflection on method and representation. This reflection has been deep and cutting, and some would argue that it has evacuated ethnography of its essence, identify and value.
  • Publication
    An analysis of genotype-phenotype maps in grammatical evolution
    We present an analysis of the genotype-phenotype map in Grammatical Evolution (GE). The standard map adopted in GE is a depth-first expansion of the non-terminal symbols during the derivation sequence. Earlier studies have indicated that allowing the path of the expansion to be under the guidance of evolution as opposed to a de- terministic process produced significant performance gains on all of the benchmark problems analysed. In this study we extend this analysis to in- clude a breadth-first and random map, investigate additional benchmark problems, and take into consideration the implications of recent results on alternative grammar representations with this new evidence. We con- clude that it is possible to improve the performance of grammar-based Genetic Programming by the manner in which a genotype-phenotype map is performed.
      574Scopus© Citations 29
  • Publication
    A Branch and Cut Algorithm for the Ring Spur Assignment Problem
    The Ring Spur Assignment Problem (RSAP) arises in the design of Next Generation Telecommunications Networks (NGNs) and has applications in location-allocation problems. The aim is to identify a minimum cost set of interconnected ring spurs. We seek to connect all nodes of the network either on a set of bounded disjoint local rings or by a single spur edge connected to a node on a local ring. Local rings are interconnected by a special ring called the tertiary ring. We show that the problem is NP-Hard and present an Integer Programming formulation with additional valid inequalities. We implement a branch-and-cut algorithm and present our conclusions with computational results.
      380Scopus© Citations 7
  • Publication
    Investigating mapping order in πGE
    We present an investigation into the genotype-phenotype map in Position Independent Grammatical Evolution (πGE). Previous studies have shown πGE to exhibit a performance increase over standard GE. The only difference between the two approaches is in how the genotype-phenotype mapping process is performed. GE uses a leftmost non terminal expansion, while πGE evolves the order of mapping as well as the content. In this study, we use the idea of focused search to examine which aspect of the πGE mapping process provides the lift in performance over standard GE by applying our approaches to four benchmark problems taken from specialised literature. We examined the traditional πGE approach and compared it to two setups which examined the extremes of mapping order search and content search, and against setups with varying ratios of content and order search. In all of these tests a purely content focused πGE was shown to exhibit a performance gain over the other setups.
      438Scopus© Citations 3
  • Publication
    A Decomposition Algorithm for the Ring Spur Assignment Problem
    This paper describes the ring spur assignment problem (RSAP), a new problem arising in the design of next generation networks. The RSAP complements the sonet ring assignment problem (SRAP). We describe the RSAP, positioning it in relation to problems previously addressed in the literature. We decompose the problem into two IP problems and describe a branch-and-cut decomposition heuristic algorithm suitable for solving problem instances in a reasonable time. We present promising computational results.
      396Scopus© Citations 5
  • Publication
    Investigation of the performance of different mapping orders for GE on the max problem
    We present an analysis of how the genotype-phenotype map in Grammatical Evolution (GE) can effect performance on the Max Problem. Earlier studies have demonstrated a performance decrease for Position independent Grammatical Evolution (πGE ) in this problem domain. In πGE the genotype-phenotype map is changed so that the evolutionary algorithm controls not only what the next expansion will be but also the choice of what position in the derivation tree is expanded next. In this study we extend previous work and investigate whether the ability to change the order of expansion is responsible for the performance decrease or if the problem is simply that a certain order of expansion in the genotype-phenotype map is responsible. We conclude that the reduction of performance in the Max problem domain by πGE is rooted in the way the genotype-phenotype map and the genetic operators used with this mapping interact.
      346Scopus© Citations 4
  • Publication
    Conceptual System Dynamics and Agent-Based Modelling Simulation of Interorganisational Fairness in Food Value Chains: Research Agenda and Case Studies
    System dynamics and agent-based simulation modelling approaches have a potential as tools to evaluate the impact of policy related decision making in food value chains. The context is that a food value chain involves flows of multiple products, financial flows and decision making among the food value chain players. Each decision may be viewed from the level of independent actors, each with their own motivations and agenda, but responding to externalities and to the behaviours of other actors. The focus is to show how simulation modelling can be applied to problems such as fairness and power asymmetries in European food value chains by evaluating the outcome of interventions in terms of relevant operational indicators of interorganisational fairness (e.g., profit distribution, market power, bargaining power). The main concepts of system dynamics and agent-based modelling are introduced and the applicability of a hybrid of these methods to food value chains is justified. This approach is outlined as a research agenda, and it is demonstrated how cognitive maps can help in the initial conceptual model building when implemented for specific food value chains studied in the EU Horizon 2020 VALUMICS project. The French wheat to bread chain has many characteristics of food value chains in general and is applied as an example to formulate a model that can be extended to capture the functioning of European FVCs. This work is to be further progressed in a subsequent stream of research for the other food value chain case studies with different governance modes and market organisation, in particular, farmed salmon to fillet, dairy cows to milk and raw tomato to processed tomato.
      60Scopus© Citations 2