SNDS Research Group

The SNDS group was established in 2014 to sustain and expand the computational mathematics and approximation theory group activities previously conducted at Stellenbosch University’s Mathematics Division under the leadership of Prof Johan de Villiers, former Research Fellow at AIMS and an Extraordinary Professor of Mathematics at Stellenbosch University. Led by Dr Rejoyce Gavhi-Molefe, the group initially concentrated on computational mathematics and approximation theory, particularly subdivision schemes, multiresolution and wavelet methods, and numerical analysis. As the field of subdivision schemes has evolved, we have expanded our research scope to include network approaches to subdivision and financial mathematics. Today, we utilise machine learning and deep learning techniques to address complex problems in subdivision and network science.
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The group’s three core research areas include:

Subdivision

Subdivision is a method for generating smooth curves and surfaces from a given sequence of data points in a plane or space. Over the last few decades, it has been developed into a fast-growing powerful tool in a variety of application areas (e.g., computer graphics, animation movie production, image processing and numerical solutions of partial differential equations). This is due to its computationally efficient properties compared to other modelling approaches for smooth curves and surfaces.

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Network Science

Network Science is an interdisciplinary field that focuses on the rigorous study of complex networks, analyzing their structure, dynamics, functions, and evolution. It investigates how nodes (representing entities such as individuals, proteins, devices, or cities) and edges (representing relationships or interactions) form interconnected systems that appear across a wide variety of domains including social, biological, technological, communication, and infrastructure networks

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Data Science

Data Science focuses on extracting meaningful insights, patterns, and knowledge from data by combining techniques from statistics, machine learning, computer science, and domain expertise. It encompasses the entire data lifecycle, including the collection, storage, cleaning, integration, analysis, and interpretation of large and often complex datasets. The goal is to transform raw data into actionable information that can support decision-making, optimization, and innovation.

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Current Research Topics

Research topics description

Wavelet decomposition and reconstruction algorithms used in signal analysis typically assume that signals are defined on the entire real line, while subdivision schemes often assume bi-infinite control point sequences. In practice, however, signals and datasets are usually finite, leading to the use of ad hoc methods that are often unsatisfactory. This research addresses the need for a systematic approach to construct wavelets on bounded intervals and subdivision schemes for finite control point sequences. Central to this work is the concept of a refinable function, which can be represented as a linear combination of integer translates of its dilation.

Building on previous work adapting the binary Dubuc–Deslauriers subdivision scheme for finite sequences, this study extends the method to general integer arity (d-ary) Dubuc–Deslauriers subdivision schemes.

Machine learning on graphs has become a central tool in modern data science, with applications in social networks, biology, chemistry, recommendation systems, and infrastructure monitoring. Despite the success of graph embeddings and Graph Neural Networks (GNNs), many existing models are biased toward local neighborhoods and may struggle to capture global, multiscale structure. This limitation becomes particularly pronounced when different networks share similar local statistics, such as degree distributions, yet differ significantly in hierarchical organization.

Fractal geometry provides a complementary perspective by characterizing networks through scale invariance, self-similarity, and multiscale complexity. Fractal descriptors such as box-counting dimension and multiscale box-cover signatures encode global structural information that is robust to local perturbations and informative under coarsegraining. This project develops a computational pipeline for fractal-aware machine learning on graphs, integrating fractal descriptors with classical machine learning models and optional GNN baselines. Through experiments on synthetic and real networks, the study evaluates when and why fractal features enhance classification, anomaly detection, and cross-domain generalization.

Curvature is a central concept in geometry, measuring how a space deviates from flatness. In Riemannian geometry, Ricci curvature governs fundamental phenomena such as volume growth, geodesic dispersion, and diffusion processes. In recent years, extending curvature concepts to discrete structures such as graphs has emerged as a powerful approach in network science, enabling a geometric understanding of complex networks. This research proposal aims to investigate Forman–Ricci curvature, a combinatorial and computationally efficient notion of Ricci curvature defined on the edges of a graph.

Starting from discrete exterior calculus and the Hodge Laplacian on graphs, the proposed research will derive the Forman–Ricci curvature formula, study its behavior in weighted and unweighted networks, and analyze its geometric interpretation in terms of local branching, expansion, and bottlenecks. Beyond the theoretical framework, the proposed work will explore applications of Forman–Ricci curvature in network analysis, including hub and bottleneck detection, robustness assessment, community structure characterization, and diffusion dynamics. The project combines rigorous mathematical foundations with computational experiments on synthetic and real-world networks, providing a geometric perspective on modern network science.

Diffusion and spreading processes on networks play a fundamental role in modeling information flow, epidemic propagation, opinion dynamics, and transport phenomena in complex systems. Classical diffusion models are typically defined on crisp or probabilistic graphs, where edges either exist or are associated with probabilities. While such models are mathematically tractable, they often fail to capture vagueness, subjectivity, and imprecision that characterize many real-world interactions. Fuzzy networks offer an alternative modeling framework in which edges are associated with degrees of membership in the interval [0, 1], representing graded interactions such as trust, influence, or confidence. This project investigates diffusion and spreading dynamics on fuzzy networks. It develops mathematical models for fuzzy diffusion, fuzzy random walks, and fuzzy contagion processes, and compares their behavior with classical crisp and probabilistic models. Through theoretical analysis and numerical simulations, the study aims to understand how fuzziness affects convergence, equilibrium, spreading speed, and robustness of diffu- sion processes

Group Members

  • Dr Rejoyce Gavhi-Molefe, AIMS South Africa
  • Prof. Franck Kalala Mutombo, University of Lubumbashi, Lubumbashi, Democratic Republic of Congo
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