Amir Shakouri, Henk J van Waarde, M Kanat Camlibel
{"title":"Chebyshev centers and radii for sets induced by quadratic matrix inequalities.","authors":"Amir Shakouri, Henk J van Waarde, M Kanat Camlibel","doi":"10.1007/s00498-025-00424-w","DOIUrl":"10.1007/s00498-025-00424-w","url":null,"abstract":"<p><p>This paper studies sets of matrices induced by quadratic inequalities. In particular, the center and radius of a smallest ball containing the set, called a <i>Chebyshev center</i> and the <i>Chebyshev radius</i>, are studied. In addition, this work studies the <i>diameter</i> of the set, which is the farthest distance between any two elements of the set. Closed-form solutions are provided for a Chebyshev center, the Chebyshev radius, and the diameter of sets induced by quadratic matrix inequalities (QMIs) with respect to arbitrary unitarily invariant norms. Examples of these norms include the Frobenius norm, spectral norm, nuclear norm, Schatten <i>p</i>-norms, and Ky Fan <i>k</i>-norms. In addition, closed-form solutions are presented for the radius of the largest ball <i>within</i> a QMI-induced set. Finally, the paper discusses applications of the presented results in data-driven modeling and control.</p>","PeriodicalId":93472,"journal":{"name":"Mathematics of control, signals, and systems : MCSS","volume":"37 4","pages":"1007-1034"},"PeriodicalIF":0.0,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12594684/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145484256","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Erasure decoding of convolutional codes using first-order representations.","authors":"Julia Lieb, Joachim Rosenthal","doi":"10.1007/s00498-021-00289-9","DOIUrl":"https://doi.org/10.1007/s00498-021-00289-9","url":null,"abstract":"<p><p>It is well known that there is a correspondence between convolutional codes and discrete-time linear systems over finite fields. In this paper, we employ the linear systems representation of a convolutional code to develop a decoding algorithm for convolutional codes over the erasure channel. In this kind of channel, which is important due to its use for data transmission over the Internet, the receiver knows if a received symbol is correct. We study the decoding problem using the state space description of a convolutional code, and this provides in a natural way additional information. With respect to previously known decoding algorithms, our new algorithm has the advantage that it is able to reduce the decoding delay as well as the computational effort in the erasure recovery process. We describe which properties a convolutional code should have in order to obtain a good decoding performance and illustrate it with an example.</p>","PeriodicalId":93472,"journal":{"name":"Mathematics of control, signals, and systems : MCSS","volume":"33 3","pages":"499-513"},"PeriodicalIF":0.0,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1007/s00498-021-00289-9","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"39642907","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}