Nick Gotts - Academia.edu (original) (raw)

Papers by Nick Gotts

Bistromathics … is … a revolutionary new way of understanding the behaviour of numbers. … Numbers... more Bistromathics … is … a revolutionary new way of understanding the behaviour of numbers. … Numbers written on restaurant bill pads within the confines of restaurants do not follow the same mathematical laws as numbers written on any other pieces of paper in any other part of the Universe. Douglas Adams, “Life, the Universe, and Everything ” (1982)

Abstract: Object-oriented (OO) programming has limitations when used to implement abstract multi-... more Abstract: Object-oriented (OO) programming has limitations when used to implement abstract multi-scale, spatially-integrated, agent-based models, that could potentially be addressed using relational databases (RDB). Although this would involve rethinking the approach to designing such models, the combined OO-RDB approach has a number of appealing advantages for multi-scale simulations, such as allowing the user rather than the programmer to specify the scale at which various land-use processes take place. It also provides a basis for a more realistic representation of the relationship between agents and their environment.

Abstract. In this paper we compare models of two different kinds of processes in multi-agentbased... more Abstract. In this paper we compare models of two different kinds of processes in multi-agentbased social simulations (MABSS): military conflict within a states-system (GeoSim), and land use and ownership change (FEARLUS). This is a kind of model-to-model comparison which is novel within Multi-Agent Based Simulation research, although well-known within mathematics, physics and biology: comparing objects (in this case MABSS) drawn from distinct research domains, in order to draw out their structural similarities and differences. This can facilitate research in both domains, by allowing the use of findings from each to illuminate the other. Based on the similarities between FEARLUS and GeoSim, we conclude by identifying a new class of MABSS models based on territorial resource allocation processes occurring on a 2-dimensional space (which we define as the “TRAP 2 ” class). The existence of the cross-domain TRAP 2 class of models in turn suggests that MABSS researchers should look for o...

Reinforcement learners tend to repeat actions that led to satisfactory outcomes in the past, and ... more Reinforcement learners tend to repeat actions that led to satisfactory outcomes in the past, and avoid choices that resulted in unsatisfactory experiences. This behavior is one of the most widespread adaptation mechanisms in nature. In this paper we fully characterize the dynamics of one of the best known stochastic models of reinforcement learning [Bush, R., Mosteller, F., 1955. Stochastic Models of Learning. Wiley & Sons, New York] for 2-player 2-strategy games. We also provide some extensions for more general games and for a wider class of learning algorithms. Specifically, it is shown that the transient dynamics of Bush and Mosteller's model can be substantially different from its asymptotic behavior. It is also demonstrated that in general-and in sharp contrast to other reinforcement learning models in the literature-the asymptotic dynamics of Bush and Mosteller's model cannot be approximated using the continuous time limit version of its expected motion.

We report results from roughly 20,000 runs of a coupled agent-based model of land use change and ... more We report results from roughly 20,000 runs of a coupled agent-based model of land use change and species metacommunity model. We explored the effect of increasing government incentive to improve biodiversity, in the context of other influences on land manager decision making: aspirations, input costs, and price variability. The experiments test four kinds of policy varying along two dimensions: activity-versus-outcome-based incentive, and individual-versus-collective incentive. The results reveal critical thresholds in incentive schemes, where a sudden increase in environmental benefit occurs for a small increase in incentive. Further, the context affects the level of incentive at which tipping points occur, and the degree of effect. Variability in outcome can also change with incentive and context, and some evidence suggests that environmental benefits are not monotone increasing functions of incentives. Intuitively, if the incentive signal is large enough, land managers will farm ...

Source code used to create every figure in the paper: Izquierdo, S. S., Izquierdo, L. R. and Gott... more Source code used to create every figure in the paper: Izquierdo, S. S., Izquierdo, L. R. and Gotts, N. M. (2008). Reinforcement Learning Dynamics in Social Dilemmas. Journal of Artificial Societies and Social Simulation 11(2)1.

Ecological Complexity, 2018

Socio-Ecological Systems (SESs) are the systems in which our everyday lives are embedded, so unde... more Socio-Ecological Systems (SESs) are the systems in which our everyday lives are embedded, so understanding them is important. The complex properties of such systems make modelling an indispensable tool for their description and analysis. Human actors play a pivotal role in SESs, but their interactions with each other and their environment are often underrepresented in SES modelling. We argue that more attention should be given to social aspects in models of SESs, but this entails additional kinds of complexity. Modelling choices need to be as transparent as possible, and to be based on analysis of the purposes and limitations of modelling. We recommend thinking in terms of modelling projects rather than single models. Such a project may involve multiple models adopting di↵erent modelling methods. We argue that agent-based models (ABMs) are an essential tool in an SES modelling project, but their expressivity, which is their major advantage, also produces problems with model transparency and validation. We propose the use of formal ontologies to make the structure and meaning of models as explicit as possible, facilitating model design, implementation, assessment, comparison and extension.

Journal of Artificial Societies and Social Simulation, 2017

The CEDSS-. agent-based model of domestic energy demand at community level is described. CEDSS (C... more The CEDSS-. agent-based model of domestic energy demand at community level is described. CEDSS (Community Energy Demand Social Simulator) is focused on household decisions (the model's agents are households) to buy energy-using appliances, heating systems, and insulation, over the period from to. Its empirical basis is a survey of households in Aberdeen and Aberdeenshire, Scotland, carried out in , combined with publicly available data on household finances and equipment, and energy prices. CEDSS-. emphasises mechanisms concerning value-strength dynamics and goal selection which influence such decisions, drawing on goal-framing theory. Results of experiments with the model are presented; the most important parameters for determining energy demand turn out to be economic (rates of change of incomes and of fuel prices), and the presence or absence of external (extra-community) influences on value-strengths. However, the value-strength dynamics used led in most runs to a single set of values dominating the population by âĂŞ but even with identical parameters, di erent sets of values could become dominant, and which did so made a very considerable di erence to demand. This resulted in bimodal distributions of outcome measures across the runs using a given parameter-setting in many cases; initial experiments indicated that changing parameters determining how far households influence each others' values could at least reduce this tendency. Issues in the analysis of complex models with aspects unconstrained by either data or theory are discussed in the final section.

Object-oriented (OO) programming has limitations when used to implement abstract multi-scale, spa... more Object-oriented (OO) programming has limitations when used to implement abstract multi-scale, spatially-integrated, agent-based models, that could potentially be addressed using relational databases (RDB). Although this would involve rethinking the approach to designing such models, the combined OO-RDB approach has a number of appealing advantages for multi-scale simulations, such as allowing the user rather than the programmer to specify the scale at which various land-use processes take place. It also provides a basis for a more realistic representation of the relationship between agents and their environment.

Lecture Notes in Economics and Mathematical Systems, 2006

This paper characterises the transient dynamics and the long-term behaviour of a game theoretical... more This paper characterises the transient dynamics and the long-term behaviour of a game theoretical model where players' decisions at any particular time are guided by a single similar situation they experienced in the pasta simple form of casebased reasoning. The transient dynamics of the model are very dependent on the process by which players learn how to play the game in any given situation. The long-run behaviour of the model varies significantly depending on whether players can occasionally explore different actions or not. When the probability of experimentation is small but non-zero, only a subset of the outcomes that are possible in the absence of experimentation persists in the long-run. In this paper we present some features that characterise such a subset of stochastically stable outcomes. 1 Common knowledge of rationality means that every player assumes: (a) that all players are instrumentally rational, and (b) that all players are aware of other players' rationalityrelated assumptions (this produces an infinite recursion of shared assumptions).

Environmental Modelling & Software, 2006

Floating point arithmetic is a subject all too often ignored, yet, for agent-based models in part... more Floating point arithmetic is a subject all too often ignored, yet, for agent-based models in particular, it has the potential to create misleading results, and even to influence emergent outcomes of the model. Using a simple demonstration model, this paper illustrates the problems that accumulated floating point errors can cause, and compares a number of techniques that might be used to address them. We show that inexact representation of parameter values, imprecision in calculation results, and differing implementations of mathematical expressions can significantly influence the behaviour of the model, and create issues for replicating results, though they do not necessarily do so. None of the techniques offer a failsafe approach that can be applied in any situation, though interval arithmetic is the most promising.

Proc. 2nd Int. Conf. European Social Simulation …, 2004

Page 1. Modelling Size Distributions of Rural Land Holdings in Scotland Nicholas M. Gotts1 and Da... more Page 1. Modelling Size Distributions of Rural Land Holdings in Scotland Nicholas M. Gotts1 and Dawn C. Parker2 Abstract. The paper reports ongoing investigations on the size distribution of rural land holdings in the real world ...

This paper presents a study on the role of adaptation and the effects of other intrinsic motivati... more This paper presents a study on the role of adaptation and the effects of other intrinsic motivations in addition to the economic payoffs in social dilemmas. Social dilemmas are modelled in an abstract way using a game-theoretic framework and agent-based modelling. The role of adaptation is studied by implementing agents that use case-based reasoning in their decision making algorithm. The effects of other intrinsic motivations are explored by introducing a certain preference for social approval that makes the agents be slightly more inclined to cooperate. The experiments conducted reveal a new concept of equilibrium characterised by the fact that no player can be guaranteed a higher payoff by changing their decision. It is proved that there is a broad range of adaptive decision- making algorithms for which such concept of equilibrium can be relevant.

The paper concerns the socio-spatial dynamics of imitation within a computational model of land u... more The paper concerns the socio-spatial dynamics of imitation within a computational model of land use selection and change. Specifically, it reports investigations of the success of imitation in relation to alternative ways of choosing a course of action, in the context of different degrees and kinds of spatio-temporal heterogeneity. Simulation experiments with the model are the main method employed, but analytical work is also reported.

Applet to replicate the experiments conducted in the paper: Izquierdo, S. S., Izquierdo, L. R. an... more Applet to replicate the experiments conducted in the paper: Izquierdo, S. S., Izquierdo, L. R. and Gotts, N. M. (2008). Reinforcement Learning Dynamics in Social Dilemmas. Journal of Artificial Societies and Social Simulation 11(2)1.

New Constructions in Cellular Automata, 2003

The construction problems and techniques described in this chapter arose out of a single problem:... more The construction problems and techniques described in this chapter arose out of a single problem: . . . What happens in very low density infinite random arrays of Conway’s Game of Life? . . . However, the work reported has wider implications, briefly discussed in the final section. Conway’s Game of Life (henceforth GoL) is a deterministic cellular automaton (CA), which is binary (a cell has two possible states: 0 and 1) and runs on an infinite two-dimensional grid of cells. A deterministic CA cell’s state at time step t is determined, according to a transition rule, by those of a set of in-neighbors at step t — 1, and its own state at step t — 1 can affect the state of i out-neighbors at t. In GoL, in-neighbors and out-neighbors coincide, and include the cell itself. The neighborhood is a 3 x 3 square of cells. GoL’s transition rule specifies that a cell is in state 1 at step t if and only if either of the following held at t - 1. 1. The cell and either two or three other cells in i...

Review of:Wilson, Alan (ed.) (2016) Global Dynamics: Approaches from Complexity Science (Wiley Se... more Review of:Wilson, Alan (ed.) (2016) Global Dynamics: Approaches from Complexity Science (Wiley Series in Computational and Quantitative Social Science). WileyBlackwell: Hoboken, NJ

Advances in Intelligent Systems and Computing, 2017

This chapter compares four implementations of (Lindenberg and Steg, J Soc Issues 63(1):117–137, 2... more This chapter compares four implementations of (Lindenberg and Steg, J Soc Issues 63(1):117–137, 2007) Goal-Framing Theory of everyday pro-environmental behaviour. Two are from different versions of CEDSS (Community Energy Demand Social Simulator, versions 3.3 and 3.4); the other two are different versions of a completely different model that also draws on Goal-Framing Theory (Rangoni and Jager, Modeling social phenomena in spatial context. Lit Verlag, Zurich, Switzerland, 2013). We find that despite some similarities in the models, the implementations are different in a number of important ways, driven in part by the case studies to which they are applied, but also by areas where Goal-Framing Theory doesn’t specify any mechanism. We anticipate that as more and more agent-based models draw on social theories, comparisons such as that herein will enable advances in both modelling and the social sciences.

The paper reports work on the topological formalism `RCC", a region-based `calculus ofconnec... more The paper reports work on the topological formalism `RCC", a region-based `calculus ofconnection" developed at Leeds university over the past several years. Specifically, it is shownthat the nonempty regular closed sets of a class of topological spaces (connected T3 -spaces)provide models for the RCC axiom-set. A brief assessment is made of RCC's potential as aformalism for applications in the area

IOP Conference Series: Earth and Environmental Science, 2009

The EU aims to develop a sustainable and secure supply of renewable energy for its citizens, layi... more The EU aims to develop a sustainable and secure supply of renewable energy for its citizens, laying foundations for a 'post-carbon' society, where greenhouse gas emissions are dramatically reduced (Commission of the European Communities, 2006). In Europe, about 35% of all primary energy use and 40% of all greenhouse gas emissions come from private households-with regional differences (Mäenpää 2005, Weber and Perrels 2000). The research planned in GILDED targets socioeconomic , cultural and political influences on individual and household energy consumption. While technological innovations can reduce the energy requirement for specific activities, and make low-carbon energy sources economically and environmentally viable, their impact in reducing emissions will depend critically on public and political commitment, without which increased energy efficiency may simply raise demand for energy-intensive products and services. GILDED will combine theoretical perspectives from environmental psychology, sociology, and political science to examine the interactions between socioeconomic , cultural and political factors in determining household energy demand and use, and conditions for the success of community-scale initiatives and experiments to reduce them. A comparative approach will be taken: between urban and rural communities; between countries in western and in central Europe (Hungary, the Czech Republic, Germany, The Netherlands and the UK), which have followed very different political, socioeconomic and cultural trajectories since World War 2; and between different kinds of energy reduction initiative. Both direct effects (externalities of individual or household consumption activities like heating, cooking and driving) and indirect effects (those that are directly caused by other actors such as businesses or state agencies, but result from serving consumers' needs and wants) will be considered. Purchases and forms of use are embedded in people's lifestyles: patterns of social situation, social practices, attitudes and values at the meso-level of social systems. (Individual behaviours, routines and tastes are micro-level, general or average ways of doing things macro-level.) Lifestyle groups are differentiated by a combination of income level and values; in some lifestyle groups, sustainable use of energy is already accepted as an important goal (Dobson 2000). We will investigate how membership in a lifestyle group is acquired, reproduced, and lost, how individuals of different groups influence each other, resulting in the evolution of lifestyle standards, and what these dynamics mean for carbon-intensive energy use. Lifestyle choices are embedded in social, cultural and political contexts: these will be addressed through analysis of the structural factors and institutional actors impacting on individual and household energy-related opportunities and limitations. Access to data on these structures will be facilitated by participants in these governance and infrastructure support networks, facilitated through stakeholder advisory groups. Here we will address governance networks, including local, city and regional government, and large-scale influences (e.g. national or EU level), and their interactions with the corporate sector, and civil society actors such as NGOs and pressure groups. Political, socioeconomic and cultural power relation structures will be examined. In addition, we will take into account that actors are embedded not only in governance structures and systems of power relations, but also in specific, socially shaped, physical environments, and materialized and institutionalized transport and provisioning networks. The research findings on lifestyle and structural issues will be integrated and utilised to inform individual case studies of energy-related policy or grassroots initiatives in each study country, thus revealing mechanisms through which energy-related behaviours can be influenced. Stakeholder advisory groups will guide the selection of an intervention of particular local interest (a past or existing initiative where possible, otherwise a potential one), ensuring that resultant findings are directly applicable to local policy concerns. Principles derived from the lifestyle, structural and initiative studies will be utilised to structure agent-based models of policy implementation and change response. Clusters of linked scenarios will be explored, each cluster focused on the role a specific type of policy instrument should play in reducing demand for carbonintensive energy within the EU, over the period to 2050. Specific policy recommendations with respect to