{"title":"Rapture of the Deep: Highs and lows of sparsity in a world of depths","authors":"Rémi Gribonval;Elisa Riccietti;Quoc-Tung Le;Léon Zheng","doi":"10.1109/MSP.2025.3611564","DOIUrl":"https://doi.org/10.1109/MSP.2025.3611564","url":null,"abstract":"Promoting sparsity in deep networks is a natural way to control their complexity, and it is a timely endeavor since practical neural model sizes have grown to unprecedented levels. The lessons from sparsity in linear inverse problems also bear the promise of many other benefits beyond such computational aspects, from statistical significance to explainability. Can these promises be fulfilled? Can we safely leverage the know-how of sparsity-promoting regularizers for inverse problems to harness sparsity in deeper contexts, linear or not? This article surveys the curses and blessings of deep sparsity. After a reminder on the main lessons from inverse problems, we tour a number of results that challenge their immediate deep extensions, from both a mathematical and a computational perspective. In particular, we highlight that <inline-formula><tex-math>${mathit{ell}}^{1}$</tex-math></inline-formula> regularization does not always lead to sparsity, and that optimization with a prescribed set of allowed nonzero coefficients can be NP-hard. We emphasize the role of rescaling invariances in these phenomena and the need to favor structured sparsity to keep sparse network training problems under control, ensure their stability, and actually enable efficient network implementations on GPUs. We finally outline the promises and challenges of a flexible family of <italic>Kronecker sparsity structures</i>, which extend the classical butterfly structure and appear in many classical scientific computing applications and that have also recently emerged in deep learning.","PeriodicalId":13246,"journal":{"name":"IEEE Signal Processing Magazine","volume":"43 2","pages":"10-23"},"PeriodicalIF":9.6,"publicationDate":"2026-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147665344","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"SPS Advance Your Career","authors":"","doi":"10.1109/MSP.2026.3676841","DOIUrl":"https://doi.org/10.1109/MSP.2026.3676841","url":null,"abstract":"","PeriodicalId":13246,"journal":{"name":"IEEE Signal Processing Magazine","volume":"43 2","pages":"C3-C3"},"PeriodicalIF":9.6,"publicationDate":"2026-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=11480034","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147665475","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Martina Pastorino;Gabriele Moser;Sebastiano B. Serpico;Josiane Zerubia
{"title":"Probabilistic Graphical Models Meet Deep Learning for Semantic Segmentation: Mathematical connections and recent developments","authors":"Martina Pastorino;Gabriele Moser;Sebastiano B. Serpico;Josiane Zerubia","doi":"10.1109/MSP.2025.3648958","DOIUrl":"https://doi.org/10.1109/MSP.2025.3648958","url":null,"abstract":"Semantic segmentation, also known as <italic>spatially dense image classification</i>, plays a crucial role in image analysis, bridging the fields of image processing and machine learning. It has wide applications, ranging from land cover mapping in Earth observation to medical diagnostics using biomedical images, fault detection in industrial imagery, and so on. This article focuses on the mathematical connections between two pivotal families of methodological approaches—probabilistic graphical models (PGMs) and deep learning (DL)—and explores the potential of their integration for semantic segmentation tasks. After providing a comprehensive overview of state-of-the-art techniques from both families, the article highlights recent developments that combine these approaches, either through theoretical equivalence or direct integration. Examples of results are provided for renowned benchmark datasets in computer vision and remote sensing, and the article concludes with a discussion of promising future research directions.","PeriodicalId":13246,"journal":{"name":"IEEE Signal Processing Magazine","volume":"43 2","pages":"51-63"},"PeriodicalIF":9.6,"publicationDate":"2026-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147665289","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"The Nasreddin Hodja Principle and the Mathematics of Deep Learning [From the Editor]","authors":"Tülay Adali","doi":"10.1109/MSP.2026.3676148","DOIUrl":"https://doi.org/10.1109/MSP.2026.3676148","url":null,"abstract":"","PeriodicalId":13246,"journal":{"name":"IEEE Signal Processing Magazine","volume":"43 2","pages":"3-4"},"PeriodicalIF":9.6,"publicationDate":"2026-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=11480039","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147665337","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Continual Learning Through the Lens of Adaptive Filtering: A mathematical tutorial","authors":"Liangzu Peng;René Vidal","doi":"10.1109/MSP.2026.3657516","DOIUrl":"https://doi.org/10.1109/MSP.2026.3657516","url":null,"abstract":"Continual learning refers to the problem of learning multiple tasks presented sequentially to the learner without forgetting previously learned tasks. Recently, many deep learning-based approaches have been proposed for continual learning; however, the mathematical foundations behind existing continual learning methods remain underdeveloped. On the other hand, adaptive filtering is a classic subject in signal processing with a rich history of mathematically principled methods. However, its role in understanding the foundations of continual learning has been underappreciated. In this tutorial, we review the basic principles behind both continual learning and adaptive filtering and present a comparative analysis that highlights multiple connections between them. These connections allow us to enhance the mathematical foundations of continual learning based on existing results for adaptive filtering, extend adaptive filtering insights using existing continual learning methods, and discuss a few research directions for continual learning suggested by the historical developments in adaptive filtering.","PeriodicalId":13246,"journal":{"name":"IEEE Signal Processing Magazine","volume":"43 2","pages":"24-36"},"PeriodicalIF":9.6,"publicationDate":"2026-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147665476","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Flow-Based Generative Models as Iterative Algorithms in Probability Space: An intuitive mathematical framework [Special Issue on the Mathematics of Deep Learning]","authors":"Yao Xie;Xiuyuan Cheng","doi":"10.1109/MSP.2025.3609527","DOIUrl":"https://doi.org/10.1109/MSP.2025.3609527","url":null,"abstract":"Flow-based generative models have emerged as a powerful class of deep generative models, offering exact likelihood estimation, invertible sample transformations, and reliable and efficient sampling, making them particularly well-suited for applications in signal processing, anomaly detection, and structured data synthesis. Unlike diffusion models, which rely on stochastic differential equations (SDEs) for progressive denoising, flow-based models define deterministic transformations governed by ordinary differential equations (ODEs), allowing for faster inference and interpretable probabilistic modeling. This tutorial presents a rigorous mathematical framework for flow-based generative models, positioning them as iterative algorithms in probability space and exploring their connections to optimal transport and Wasserstein gradient flows. We discuss key algorithmic insights, including continuous normalizing flows (CNFs), flow-matching (FM), and distributionally robust optimization (DRO), which enable efficient, high-dimensional generative modeling with theoretical guarantees. We also examine the role of flow-based models in progressive training schemes, demonstrating their convergence properties and generative guarantees under structured optimization frameworks. By bridging mathematical theory with practical implementation, this tutorial aims to provide researchers and practitioners with a comprehensive foundation in flow-based generative modeling and its applications in signal processing and beyond.","PeriodicalId":13246,"journal":{"name":"IEEE Signal Processing Magazine","volume":"43 2","pages":"37-50"},"PeriodicalIF":9.6,"publicationDate":"2026-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147665512","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Random Matrix Theory for Deep Learning: Beyond Eigenvalues of Linear Models [Special Issue on the Mathematics of Deep Learning]","authors":"Zhenyu Liao;Michael W. Mahoney","doi":"10.1109/MSP.2025.3618012","DOIUrl":"https://doi.org/10.1109/MSP.2025.3618012","url":null,"abstract":"Modern machine learning (ML) and deep neural networks (DNNs) often operate on high-dimensional data and rely on overparameterized models, where classical low-dimensional intuitions break down. In particular, the proportional regime where the data dimension, sample size, and number of model parameters are all large and comparable, gives rise to novel and sometimes counterintuitive behaviors. This article extends traditional random matrix theory (RMT) beyond eigenvalue-based analysis of linear models to address the challenges posed by nonlinear ML models such as DNNs in this regime. We introduce the concept of high-dimensional equivalent, which unifies and generalizes both deterministic equivalent and linear equivalent, to systematically address three technical challenges: high dimensionality, nonlinearity, and the need to analyze generic eigenspectral functionals. Leveraging this framework, we provide precise characterizations of the training and generalization performance of linear models, nonlinear shallow networks, and deep networks. Our results capture rich phenomena, including scaling laws, double descent, and nonlinear learning dynamics, offering a unified perspective on the theoretical understanding of deep learning in high dimensions.","PeriodicalId":13246,"journal":{"name":"IEEE Signal Processing Magazine","volume":"43 2","pages":"93-106"},"PeriodicalIF":9.6,"publicationDate":"2026-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147696206","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}