no code implementations • 18 Mar 2024 • Dimitrios G. Patsatzis, Lucia Russo, Constantinos Siettos
We present a physics-informed neural network (PINN) approach for the discovery of slow invariant manifolds (SIMs), for the most general class of fast/slow dynamical systems of ODEs.
no code implementations • 19 Feb 2024 • Hector Vargas Alvarez, Gianluca Fabiani, Ioannis G. Kevrekidis, Nikolaos Kazantzis, Constantinos Siettos
We use Physics-Informed Neural Networks (PINNs) to solve the discrete-time nonlinear observer state estimation problem.
no code implementations • 25 Sep 2023 • Gianluca Fabiani, Nikolaos Evangelou, Tianqi Cui, Juan M. Bello-Rivas, Cristina P. Martin-Linares, Constantinos Siettos, Ioannis G. Kevrekidis
We present a machine learning (ML)-assisted framework bridging manifold learning, neural networks, Gaussian processes, and Equation-Free multiscale modeling, for (a) detecting tipping points in the emergent behavior of complex systems, and (b) characterizing probabilities of rare events (here, catastrophic shifts) near them.
no code implementations • 14 Sep 2023 • Dimitrios G. Patsatzis, Gianluca Fabiani, Lucia Russo, Constantinos Siettos
A comparison of the computational costs between symbolic, automatic and numerical approximation of the required derivatives in the learning process is also provided.
no code implementations • 24 Apr 2023 • Ioannis K. Gallos, Daniel Lehmberg, Felix Dietrich, Constantinos Siettos
Importantly, we show that the proposed Koopman operator approach provides, for any practical purposes, equivalent results to the FNN-GH approach, thus bypassing the need to train a non-linear map and to use GH to extrapolate predictions in the ambient fMRI space; one can use instead the low-frequency truncation of the DMs function space of L^2-integrable functions, to predict the entire list of coordinate functions in the fMRI space and to solve the pre-image problem.
no code implementations • 15 Mar 2023 • Hector Vargas Alvarez, Gianluca Fabiani, Nikolaos Kazantzis, Constantinos Siettos, Ioannis G. Kevrekidis
We assess the performance of the proposed PIML approach via a benchmark nonlinear discrete map for which the feedback linearization transformation law can be derived analytically; the example is characterized by steep gradients, due to the presence of singularities, in the domain of interest.
no code implementations • 12 Jul 2022 • Dimitrios G. Patsatzis, Lucia Russo, Ioannis G. Kevrekidis, Constantinos Siettos
We present an Equation/Variable free machine learning (EVFML) framework for the control of the collective dynamics of complex/multiscale systems modelled via microscopic/agent-based simulators.
no code implementations • 10 Mar 2022 • Gianluca Fabiani, Evangelos Galaris, Lucia Russo, Constantinos Siettos
The unknown weights between the hidden and output layer are computed by Newton's iterations, using the Moore-Penrose pseudoinverse for low to medium, and sparse QR decomposition with regularization for medium to large scale systems.
no code implementations • 31 Jan 2022 • Evangelos Galaris, Gianluca Fabiani, Ioannis Gallos, Ioannis Kevrekidis, Constantinos Siettos
For our illustrations, we implemented the proposed method to construct the one-parameter bifurcation diagram of the 1D FitzHugh-Nagumo PDEs from data generated by $D1Q3$ Lattice Boltzmann simulations.
no code implementations • 7 Oct 2021 • Panagiotis Papaioannou, Ronen Talmon, Ioannis Kevrekidis, Constantinos Siettos
We address a three-tier numerical framework based on manifold learning for the forecasting of high-dimensional time series.
no code implementations • 3 Aug 2021 • Evangelos Galaris, Gianluca Fabiani, Francesco Calabrò, Daniela di Serafino, Constantinos Siettos
We propose a numerical method based on physics-informed Random Projection Neural Networks for the solution of Initial Value Problems (IVPs) of Ordinary Differential Equations (ODEs) with a focus on stiff problems.
no code implementations • 20 Jul 2021 • Konstantinos Spiliotis, Giannis Kahramanoglou, Jens Starke, Nikolaos Smyrnis, Constantinos Siettos
We address a biophysical network dynamical model to study how the modulation of dopamine (DA) activity and related N-methyl-d-aspartate (NMDA) glutamate receptor activity as well as the emerging Pre-Frontal Cortex (PFC) functional connectivity network (FCN) affect inhibitory cognitive function in schizophrenia in an antisaccade task.
no code implementations • 10 Dec 2020 • Francesco Calabrò, Gianluca Fabiani, Constantinos Siettos
We show that a feedforward neural network with a single hidden layer with sigmoidal functions and fixed, random, internal weights and biases can be used to compute accurately a collocation solution.
Numerical Analysis Numerical Analysis
no code implementations • 25 May 2020 • Ioannis Gallos, Evangelos Galaris, Constantinos Siettos
We construct embedded functional connectivity networks (FCN) from benchmark resting-state functional magnetic resonance imaging (rsfMRI) data acquired from patients with schizophrenia and healthy controls based on linear and nonlinear manifold learning algorithms, namely, Multidimensional Scaling (MDS), Isometric Feature Mapping (ISOMAP) and Diffusion Maps.