Search Results for author: Themistoklis P. Sapsis

Found 13 papers, 5 papers with code

Evaluation of machine learning architectures on the quantification of epistemic and aleatoric uncertainties in complex dynamical systems

no code implementations27 Jun 2023 Stephen Guth, Alireza Mojahed, Themistoklis P. Sapsis

Machine learning methods for the construction of data-driven reduced order model models are used in an increasing variety of engineering domains, especially as a supplement to expensive computational fluid dynamics for design problems.

Gaussian Processes Uncertainty Quantification

Active Learning for Optimal Intervention Design in Causal Models

1 code implementation10 Sep 2022 JiaQi Zhang, Louis Cammarata, Chandler Squires, Themistoklis P. Sapsis, Caroline Uhler

Here, we develop a causal active learning strategy to identify interventions that are optimal, as measured by the discrepancy between the post-interventional mean of the distribution and a desired target mean.

Active Learning Experimental Design

Discovering and forecasting extreme events via active learning in neural operators

no code implementations5 Apr 2022 Ethan Pickering, Stephen Guth, George Em Karniadakis, Themistoklis P. Sapsis

This model-agnostic framework pairs a BED scheme that actively selects data for quantifying extreme events with an ensemble of DNOs that approximate infinite-dimensional nonlinear operators.

Active Learning Experimental Design +1

Machine-learning energy-preserving nonlocal closures for turbulent fluid flows and inertial tracers

no code implementations15 Feb 2021 Alexis-Tzianni G. Charalampopoulos, Themistoklis P. Sapsis

Overall the adoption of the constraint results in an average improvement of 26% for one-dimensional closures and 29% for two-dimensional closures, being notably larger for flows that were not used for training.

Fluid Dynamics

Sparse Methods for Automatic Relevance Determination

1 code implementation18 May 2020 Samuel H. Rudy, Themistoklis P. Sapsis

This work considers methods for imposing sparsity in Bayesian regression with applications in nonlinear system identification.

regression

Backpropagation Algorithms and Reservoir Computing in Recurrent Neural Networks for the Forecasting of Complex Spatiotemporal Dynamics

1 code implementation9 Oct 2019 Pantelis R. Vlachas, Jaideep Pathak, Brian R. Hunt, Themistoklis P. Sapsis, Michelle Girvan, Edward Ott, Petros Koumoutsakos

We examine the efficiency of Recurrent Neural Networks in forecasting the spatiotemporal dynamics of high dimensional and reduced order complex systems using Reservoir Computing (RC) and Backpropagation through time (BPTT) for gated network architectures.

Learning the Tangent Space of Dynamical Instabilities from Data

1 code implementation24 Jul 2019 Antoine Blanchard, Themistoklis P. Sapsis

For a large class of dynamical systems, the optimally time-dependent (OTD) modes, a set of deformable orthonormal tangent vectors that track directions of instabilities along any trajectory, are known to depend "pointwise" on the state of the system on the attractor, and not on the history of the trajectory.

Output-weighted optimal sampling for Bayesian regression and rare event statistics using few samples

no code implementations17 Jul 2019 Themistoklis P. Sapsis

For many important problems the quantity of interest is an unknown function of the parameters, which is a random vector with known statistics.

Active Learning Experimental Design +1

A sequential sampling strategy for extreme event statistics in nonlinear dynamical systems

no code implementations19 Apr 2018 Mustafa A. Mohamad, Themistoklis P. Sapsis

The 'next-best' design point is sequentially determined through an optimization procedure that selects the point in parameter space that maximally reduces uncertainty between the estimated bounds of the pdf prediction.

Bayesian Inference

Data-assisted reduced-order modeling of extreme events in complex dynamical systems

1 code implementation9 Mar 2018 Zhong Yi Wan, Pantelis R. Vlachas, Petros Koumoutsakos, Themistoklis P. Sapsis

In this way, the data-driven model improves the imperfect model in regions where data is available, while for locations where data is sparse the imperfect model still provides a baseline for the prediction of the system dynamics.

Chaotic Dynamics Computational Physics

Data-Driven Forecasting of High-Dimensional Chaotic Systems with Long Short-Term Memory Networks

no code implementations21 Feb 2018 Pantelis R. Vlachas, Wonmin Byeon, Zhong Y. Wan, Themistoklis P. Sapsis, Petros Koumoutsakos

We introduce a data-driven forecasting method for high-dimensional chaotic systems using long short-term memory (LSTM) recurrent neural networks.

Gaussian Processes Time Series +1

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