This book constitutes revised selected papers from the 13th International Conference on Large-Scale Scientific Computing, LSSC 23021, which was held in Sozopol, Bulgaria, during June 7-11, 2021.

The 60 papers included in this book were carefully reviewed and selected from a total of 73 submissions. The volume also includes two invited talks in full paper length. The papers were organized in topical sections as follows: Fractional diffusion problems: numerical methods, algorithms and applications; large-scale models: numerical methods, parallel computations and applications; application of metaheuristics to large-scale problems; advanced discretizations and solvers for coupled systems of partial differential equations; optimal control of ODEs, PDEs and applications; tensor and matrix factorization for big-data analysis; machine learning and model order reduction for large scale predictive simulations; HPC and big data: algorithms and applications; and contributed papers.

Invited Papers.- Random-walk Based Approximate k-Nearest Neighbors Algorithm for Diffusion State Distance.- Model Reduction for Large Scale Systems.- II Fractional Di_usion Problems: Numerical Methods, Algorithms and Applications.- Constructions of Second Order Approximations of the Caputo Fractional Derivative.- Parameter Identification Approach for a Fractional Dynamics Model of Honeybee Population.- A Newton's Method for Best Uniform Polynomial Approximation.- Reduced Sum Implementation of the BURA Method for Spectral Fractional Diffusion Problems.- First-order Reaction-diffusion System with Space-fractional Diffusion in an Unbounded medium.- Performance Study of Hierarchical Semi-Separable Compression Solver for Parabolic Problems with Space-fractional Diffusion.- Numerical Solution of Non-Stationary Problems with a Rational Approximation for Fractional Powers of the Operator.- Large-Scale Models: Numerical Methods, Parallel Computations and Applications.- An Exact Schur ComplementMethod for Time-harmonic Optimal Control Problems.- On the Consistency Order of Runge-Kutta Methods Combined with Active Richardson Extrapolation.- Study the Recurrence of the Dominant Pollutants in the Formation of AQI Status Over the City of Sofia for the Period 2013-2020.- One Solution of Task with Internal Flow in Non-uniform Fluid Using CABARET Method.- Behavior and Scalability of the Regional Climate Model RegCM4 on High Performance Computing Platforms.- Quantum Effects on 1/2[111] Edge Dislocation Motion in Hydrogen-Charged Fe from Ring-Polymer Molecular Dynamics.- Degeneracy of Tetrahedral Partitions Produced by Randomly Generated Red Refinements.- Effluent Recirculation for Contaminant Removal in Constructed Wetlands under Uncertainty: A Stochastic Numerical Approach Based on Monte Carlo Methodology.- Sensitivity Study of Large-Scale Air Pollution Model Based on Modifications of the Latin Hypercube Sampling Method.- Sensitivity Operator-Based Approach to the Interpretation ofHeterogeneous Air Quality Monitoring Data.- Using the Cauchy Criterion and the Standard Deviation to Evaluate the Sustainability of Climate Simulations.- Multidimensional Sensitivity Analysis of an Air Pollution Model Based on Modifications of the van der Corput Sequence.- Running an Atmospheric Chemistry Scheme from a Large Air Pollution Model by Using Advanced Versions of the Richardson Extrapolation.- Application of Metaheuristics to Large-Scale Problems.- New Clustering Techniques of Node Embeddings Based on Metaheuristic Optimization Algorithms.- A Comparison of Machine Learning Methods for Forecasting Dow Jones Stock Index.- Optimal Knockout Tournaments: Definition and Computation.- Risk Registry Platform for Optimizations in Cases of CBRN and Critical Infrastructure Attacks.- Influence of the ACO Evaporation Parameter for Unstructured Workforce Planning Problem.- binMeta:

a New Java Package for Meta-heuristic Searches.- Synergy between Convergence and Divergence - Review of Concepts and Methods.- Advanced Stochastic Approaches Based on Optimization of Lattice Sequences for Large-Scale Finance Problems.- Intuitionistic Fuzzy Approach for Outsourcing Provider Selection in a Refinery.- Quantitative Relationship Between Particulate Matter and Morbidity.- Advanced Discretizations and Solvers for Coupled Systems of Partial Differential Equations.- Decoupling Methods for Systems of Parabolic Equations.- Optimal Control of ODEs, PDEs and Applications.- Random Lifting of Set-valued Maps.- Höolder Regularity in Bang-Bang Type Affine Optimal Control Problems.- Simultaneous Space-time Finite Element Methods for Parabolic Optimal Control Problems.- A New Algorithm for the LQR Problem with Partially Unknown Dynamics.- Tensor and Matrix Factorization for Big-Data Analysis.- Solving Systems of Polynomial Equations - a Tensor Approach.- Nonnegative Tensor-train Low-rank Approximations of the Smoluchowski Coagulation Equation.- Boolean Hierarchical Tucker Networks on Quantum Annealers.- Topic Analysis of Superconductivity Literature by Semantic Non-negative Matrix Factorization.- Machine Learning and Model Order Reduction for Large Scale Predictive Simulations.- Deep Neural Networks and Adaptive Quadrature for Solving Variational Problems.- A full order, reduced order and machine learning model pipeline for efficient prediction of reactive flows.- A Multiscale Fatigue Model for the Degradation of Fiber-reinforced Materials.- A Classification Algorithm for Anomaly Detection in Terahertz Tomography.- Reduced Basis Methods for Efficient Simulation of a Rigid Robot Hand Interacting with Soft Tissue.- Structured Deep Kernel Networks for Data-Driven Closure Terms of Turbulent Flows.- HPC and Big Data: Algorithms and Applications.- On the Use of Low-discrepancy Sequences in the Training of Neural Networks.- A PGAS-based Implementation for the Parallel Minimum Spanning Tree Algorithm.- Comparison of Di_erent Methods for Multiple Imputation by Chain Equation.- Monte Carlo Method for Estimating Eigenvalues Using Error Balancing.- Multi-Lingual Emotion Classification Using Convolutional Neural Networks.- On Parallel MLMC for Stationary Single Phase Flow Problem.- Numerical Parameter Estimates of Beta-uniform Mixture Models.- Large-Scale Computer Simulation of the Performance of the Generalized Nets Model of the LPF-algorithm.- Contributed Papers.- A New Error Estimate for a Primal-Dual Crank-Nicolson Mixed Finite Element Using Lowest Degree Raviart-Thomas Spaces for Parabolic Equations.- A Finite Volume Scheme for a Wave Equation with Several Time Independent Delays.- Recovering the Time-Dependent Volatility in Jump-Diffusion Models from Nonlocal Price Observations.- On the Solution of Contact Problems with Tresca Friction by the Semismooth* Newton Method.- Fitted Finite Volume Method for Unsaturated Flow Parabolic Problems with Space Degeneration.- Minimization of p-Laplacian via the Finite Element Method in MATLAB.- Quality Optimizationof Seismic-derived Surface Meshes of Geological Bodies.