arXiv subjects

Ioannis Markou

Publications and source records attributed to Ioannis Markou.

7 recordsLinked to original sources

arXiv2025

Opinion dynamics for an increasing population of agents. A symmetric continuous agent model

In this paper we formulate a continuous opinion model that takes into account population growth, i.e. increase with time in the number of interacting agents $N(t)$. In our setting the population growth is governed by a generic growth rate function $b(t, N(t))$. The two main components of our model are the growth rate $b(t, N(t))$, as well as the opinions of the incoming agents which are modeled in our system as boundary conditions in a free boundary problem. We give results on the well-posedness of the model and results that showcase how these two components affect the long time asymptotic behavior of our system. Moreover, we provide a kinetic (probabilistic) description of our model and give results on well-posedness and asymptotics for the kinetic model.

math.AP↗

arXiv2023

A simple consensus model for an increasing population of agents with i.i.d incoming opinions

In this short note we study what happens in a symmetric opinion model when we send the total interacting population $N(t)$ to infinity as $t \to \infty$. We assume that new population enters the system with opinions that are i.i.d random vectors with finite mean and variance. We give sharp conditions on the rate of population growth that is required for convergence to a global consensus in opinions. More particularly, we show that if the total population increases at a rate $N(t)\sim e^{t^\alpha}$, then $\alpha<1$ is necessary and sufficient condition for convergence to the mean of incoming opinions, and the convergence is achieved at an algebraic rate.

math.PR↗

arXiv2021

Invariance of velocity angles and flocking in the Inertial Spin model

We study the invariance of velocity angles and flocking properties of the Inertial Spin model introduced by Cavagna et al. [J. Stat. Phys., 158, (2015), 601--627]. We present a novel approach, based on a second order nonlinear Gronwall inequality for the velocity diameter, to identify invariant regions and study the flocking behavior of the model. This is an approach inspired by the work of Choi-Ha-Yun in the study of synchronization for kuramoto oscillators with finite inertia [Physica D, 240, (2011), 32--44]. We give sufficient conditions in terms of the parameters of the model and the initial data, so that invariant regions and asymptotic alignment of velocities is possible for coupling interactions that satisfy general assumptions.

math.DS↗

arXiv2020

Exponential asymptotic flocking in the Cucker-Smale model with distributed reaction delays

We study a variant of the Cucker-Smale system with distributed reaction delays. Using backward-forward and stability estimates on the quadratic velocity fluctuations we derive sufficient conditions for asymptotic flocking of the solutions. The conditions are formulated in terms of moments of the delay distribution and they guarantee exponential decay of velocity fluctuations towards zero for large times. We demonstrate the applicability of our theory to particular delay distributions - exponential, uniform and linear. For the exponential distribution, the flocking condition can be resolved analytically, leading to an explicit formula. For the other two distributions, the satisfiability of the assumptions is investigated numerically.

math.DS↗

arXiv2018

Asymptotic flocking in the Cucker-Smale model with reaction-type delays in the non-oscillatory regime

We study a variant of the Cucker-Smale system with reaction-type delay. Using novel backward-forward and stability estimates on appropriate quantities we derive sufficient conditions for asymptotic flocking of the solutions. These conditions, although not explicit, relate the velocity fluctuation of the initial datum and the length of the delay. If satisfied, they guarantee monotone decay (i.e., non-oscillatory regime) of the velocity fluctuations towards zero for large times. For the simplified setting with only two agents and constant communication rate the Cucker-Smale system reduces to the delay negative feedback equation. We demonstrate that in this case our method provides the sharp condition for the size of the delay such that the solution be non-oscillatory. Moreover, we comment on the mathematical issues appearing in the formal macroscopic description of the reaction-type delay system.

math.CA↗

arXiv2018

Collision-avoiding in the singular Cucker-Smale model with nonlinear velocity couplings

Collision avoidance is an interesting feature of the Cucker-Smale (CS) model of flocking that has been studied in many works, e.g. [1, 2, 4, 6, 7, 20, 21, 22]. In particular, in the case of singular interactions between agents, as is the case of the CS model with communication weights of the type $ψ(s)=s^{-α}$ for $α\geq 1$, it is important for showing global well-posedness of the underlying particle dynamics. In [4], a proof of the non-collision property for singular interactions is given in the case of the linear CS model, i.e. when the velocity coupling between agents $i,j$ is $v_{j}-v_{i}$. This paper can be seen as an extension of the analysis in [4]. We show that particles avoid collisions even when the linear coupling in the CS system has been substituted with the nonlinear term $Γ(\cdot)$ introduced in [12] (typical examples being $Γ(v)=v|v|^{2(γ-1)}$ for $γ\in (\frac{1}{2},\frac{3}{2})$), and prove that no collisions can happen in finite time when $α\geq 1$. We also show uniform estimates for the minimum inter-particle distance, for a communication weight with expanded singularity $ψ_δ(s)=(s-δ)^{-α}$, when $α\geq 2γ$, $δ\geq 0$.

math.CA↗

arXiv2018

Hydrodynamic Limit for a Fokker-Planck Equation with Coefficients in Sobolev Spaces

In this paper we study the hydrodynamic (small mass approximation) limit of a Fokker-Planck equation. This equation arises in the kinetic description of the evolution of a particle system immersed in a viscous Stokes flow. We discuss two different methods of hydrodynamic convergence. The first method works with initial data in a weighted L2 space and uses weak convergence and the extraction of convergent subsequences. The second uses entropic initial data and gives an L1 convergence to the solution of the limit problem via the study of the relative entropy.

math.AP↗