674,118 research outputs found
Spatial interactions in agent-based modeling
Agent Based Modeling (ABM) has become a widespread approach to model complex
interactions. In this chapter after briefly summarizing some features of ABM
the different approaches in modeling spatial interactions are discussed.
It is stressed that agents can interact either indirectly through a shared
environment and/or directly with each other. In such an approach, higher-order
variables such as commodity prices, population dynamics or even institutions,
are not exogenously specified but instead are seen as the results of
interactions. It is highlighted in the chapter that the understanding of
patterns emerging from such spatial interaction between agents is a key problem
as much as their description through analytical or simulation means.
The chapter reviews different approaches for modeling agents' behavior,
taking into account either explicit spatial (lattice based) structures or
networks. Some emphasis is placed on recent ABM as applied to the description
of the dynamics of the geographical distribution of economic activities, - out
of equilibrium. The Eurace@Unibi Model, an agent-based macroeconomic model with
spatial structure, is used to illustrate the potential of such an approach for
spatial policy analysis.Comment: 26 pages, 5 figures, 105 references; a chapter prepared for the book
"Complexity and Geographical Economics - Topics and Tools", P. Commendatore,
S.S. Kayam and I. Kubin, Eds. (Springer, in press, 2014
Higher-order Graph Convolutional Network with Flower-Petals Laplacians on Simplicial Complexes
Despite the recent successes of vanilla Graph Neural Networks (GNNs) on many
tasks, their foundation on pairwise interaction networks inherently limits
their capacity to discern latent higher-order interactions in complex systems.
To bridge this capability gap, we propose a novel approach exploiting the rich
mathematical theory of simplicial complexes (SCs) - a robust tool for modeling
higher-order interactions. Current SC-based GNNs are burdened by high
complexity and rigidity, and quantifying higher-order interaction strengths
remains challenging. Innovatively, we present a higher-order Flower-Petals (FP)
model, incorporating FP Laplacians into SCs. Further, we introduce a
Higher-order Graph Convolutional Network (HiGCN) grounded in FP Laplacians,
capable of discerning intrinsic features across varying topological scales. By
employing learnable graph filters, a parameter group within each FP Laplacian
domain, we can identify diverse patterns where the filters' weights serve as a
quantifiable measure of higher-order interaction strengths. The theoretical
underpinnings of HiGCN's advanced expressiveness are rigorously demonstrated.
Additionally, our empirical investigations reveal that the proposed model
accomplishes state-of-the-art (SOTA) performance on a range of graph tasks and
provides a scalable and flexible solution to explore higher-order interactions
in graphs
2D pattern evolution constrained by complex network dynamics
Complex networks have established themselves along the last years as being
particularly suitable and flexible for representing and modeling several
complex natural and human-made systems. At the same time in which the
structural intricacies of such networks are being revealed and understood,
efforts have also been directed at investigating how such connectivity
properties define and constrain the dynamics of systems unfolding on such
structures. However, lesser attention has been focused on hybrid systems,
\textit{i.e.} involving more than one type of network and/or dynamics. Because
several real systems present such an organization (\textit{e.g.} the dynamics
of a disease coexisting with the dynamics of the immune system), it becomes
important to address such hybrid systems. The current paper investigates a
specific system involving a diffusive (linear and non-linear) dynamics taking
place in a regular network while interacting with a complex network of
defensive agents following Erd\"os-R\'enyi and Barab\'asi-Albert graph models,
whose nodes can be displaced spatially. More specifically, the complex network
is expected to control, and if possible to extinguish, the diffusion of some
given unwanted process (\textit{e.g.} fire, oil spilling, pest dissemination,
and virus or bacteria reproduction during an infection). Two types of pattern
evolution are considered: Fick and Gray-Scott. The nodes of the defensive
network then interact with the diffusing patterns and communicate between
themselves in order to control the spreading. The main findings include the
identification of higher efficiency for the Barab\'asi-Albert control networks.Comment: 18 pages, 32 figures. A working manuscript, comments are welcome
The Clusteron: Toward a Simple Abstraction for a Complex Neuron
Are single neocortical neurons as powerful as multi-layered networks? A
recent compartmental modeling study has shown that voltage-dependent
membrane nonlinearities present in a complex dendritic tree can provide
a virtual layer of local nonlinear processing elements between synaptic inputs
and the final output at the cell body, analogous to a hidden layer
in a multi-layer network. In this paper, an abstract model neuron is introduced,
called a clusteron, which incorporates aspects of the dendritic
"cluster-sensitivity" phenomenon seen in these detailed biophysical modeling
studies. It is shown, using a clusteron, that a Hebb-type learning
rule can be used to extract higher-order statistics from a set of training
patterns, by manipulating the spatial ordering of synaptic connections
onto the dendritic tree. The potential neurobiological relevance of these
higher-order statistics for nonlinear pattern discrimination is then studied
within a full compartmental model of a neocortical pyramidal cell, using
a training set of 1000 high-dimensional sparse random patterns
Nonlinear dynamics of waves and modulated waves in 1D thermocapillary flows. I: General presentation and periodic solutions
We present experimental results on hydrothermal traveling-waves dynamics in
long and narrow 1D channels. The onset of primary traveling-wave patterns is
briefly presented for different fluid heights and for annular or bounded
channels, i.e., within periodic or non-periodic boundary conditions. For
periodic boundary conditions, by increasing the control parameter or changing
the discrete mean-wavenumber of the waves, we produce modulated waves patterns.
These patterns range from stable periodic phase-solutions, due to supercritical
Eckhaus instability, to spatio-temporal defect-chaos involving traveling holes
and/or counter-propagating-waves competition, i.e., traveling sources and
sinks. The transition from non-linearly saturated Eckhaus modulations to
transient pattern-breaks by traveling holes and spatio-temporal defects is
documented. Our observations are presented in the framework of coupled complex
Ginzburg-Landau equations with additional fourth and fifth order terms which
account for the reflection symmetry breaking at high wave-amplitude far from
onset. The second part of this paper (nlin.PS/0208030) extends this study to
spatially non-periodic patterns observed in both annular and bounded channel.Comment: 45 pages, 21 figures (elsart.cls + AMS extensions). Accepted in
Physica D. See also companion paper "Nonlinear dynamics of waves and
modulated waves in 1D thermocapillary flows. II: Convective/absolute
transitions" (nlin.PS/0208030). A version with high resolution figures is
available on N.G. web pag
Modeling of Induced Hydraulically Fractured Wells in Shale Reservoirs Using Branched Fractals
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