{"title":"Fourier-Poisson Transforms Associated with the Principal Series Representations of Sp(1, n)","authors":"Xingya Fan, Jianxun He, Xiaoke Jia","doi":"10.1007/s00006-024-01330-1","DOIUrl":"10.1007/s00006-024-01330-1","url":null,"abstract":"<div><p>Let <span>(X=Sp(1,n)/Sp(n))</span> be the quaternion hyperbolic space with a left invariant Haar measure, unique up to scalars, where <i>n</i> is greater than or equal to 1. The Fürstenberg boundary of <i>X</i> is denoted as <span>(Sigma )</span>. In this paper, we focus on the Plancherel formula on <i>X</i> associated with the Poisson transform of vector-valued <span>(L^2)</span>-space on <span>(Sigma )</span>. Through the Fourier-Jacobi transform and the Fourier-Poisson transform, we derive the Plancherel decomposition of the unitary representation of <i>Sp</i>(1, <i>n</i>) on <span>(L^2(X))</span>.</p></div>","PeriodicalId":7330,"journal":{"name":"Advances in Applied Clifford Algebras","volume":"34 3","pages":""},"PeriodicalIF":1.1,"publicationDate":"2024-05-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141165253","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Mobility Analysis of Multi-loop Coupling Mechanisms Using Geometric Algebra","authors":"Jinqun Guo, Yu Xiao, Qinchuan Li, Lingmin Xu, Xinxue Chai","doi":"10.1007/s00006-024-01329-8","DOIUrl":"10.1007/s00006-024-01329-8","url":null,"abstract":"<div><p>Multi-loop coupling mechanisms (MCMs) have been widely used in spacedeployable antennas. However, the mobility of MCMs is difficult to analyze due to their complicated structure and coupled limbs. This paper proposes a general method for calculating the mobility of MCMs using geometric algebra (GA). For the independent limbs in the MCM, the twist spaces are constructed by the join operator. For coupled limbs coupled with closed loops in the MCM, the equivalent limbs can be found by solving the analytical expressions of the twist space on each closed loop’s output link. Then, the twist spaces of the coupled limbs can be easily obtained. The twist space of the MCM’s output link is the intersection of all the limb twist spaces, which can be calculated by the meet operator. The proposed method provides a simplified way of analyzing the mobility of MCMs, and three typical MCMs are chosen to validate this method. The analytical mobility of the MCM’s output link can be obtained, and it naturally indicates both the number and the property of the degrees of freedom (DOFs).</p></div>","PeriodicalId":7330,"journal":{"name":"Advances in Applied Clifford Algebras","volume":"34 3","pages":""},"PeriodicalIF":1.1,"publicationDate":"2024-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141159673","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"On SVD and Polar Decomposition in Real and Complexified Clifford Algebras","authors":"Dmitry Shirokov","doi":"10.1007/s00006-024-01328-9","DOIUrl":"10.1007/s00006-024-01328-9","url":null,"abstract":"<div><p>In this paper, we present a natural implementation of singular value decomposition (SVD) and polar decomposition of an arbitrary multivector in nondegenerate real and complexified Clifford geometric algebras of arbitrary dimension and signature. The new theorems involve only operations in geometric algebras and do not involve matrix operations. We naturally define these and other related structures such as Hermitian conjugation, Euclidean space, and Lie groups in geometric algebras. The results can be used in various applications of geometric algebras in computer science, engineering, and physics.</p></div>","PeriodicalId":7330,"journal":{"name":"Advances in Applied Clifford Algebras","volume":"34 3","pages":""},"PeriodicalIF":1.1,"publicationDate":"2024-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141156686","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Distribution Function and Nonincreasing Rearrangement of ({mathbb {B}}{mathbb {C}})-Valued Functions with ({mathbb {B}} {mathbb {C}})-Measure","authors":"İlker Eryılmaz","doi":"10.1007/s00006-024-01327-w","DOIUrl":"10.1007/s00006-024-01327-w","url":null,"abstract":"<div><p>This paper investigates the distribution function and nonincreasing rearrangement of <span>(mathbb{B}mathbb{C})</span>-valued functions equipped with the hyperbolic norm. It begins by introducing the concept of the distribution function for <span>( mathbb{B}mathbb{C})</span>-valued functions, which characterizes valuable insights into the behavior and structure of <span>(mathbb{B}mathbb{C})</span>-valued functions, allowing to analyze their properties and establish connections with other mathematical concepts. Next, the nonincreasing rearrangement of <span>(mathbb{B}mathbb{C})</span>-valued functions with the hyperbolic norm are studied. By exploring the nonincreasing rearrangement of <span>(mathbb{B}mathbb{C})</span>-valued functions, it is aimed to determine how the hyperbolic norm influences the rearrangement process and its impact on the function’s behavior and properties.</p></div>","PeriodicalId":7330,"journal":{"name":"Advances in Applied Clifford Algebras","volume":"34 3","pages":""},"PeriodicalIF":1.1,"publicationDate":"2024-05-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00006-024-01327-w.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140954614","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Hausdorff–Young Inequalities for Fourier Transforms over Cayley–Dickson Algebras","authors":"Shihao Fan, Guangbin Ren","doi":"10.1007/s00006-024-01326-x","DOIUrl":"10.1007/s00006-024-01326-x","url":null,"abstract":"<div><p>In this study, we extend Beckner’s seminal work on the Fourier transform to the domain of Cayley–Dickson algebras, establishing a precise form of the Hausdorff–Young inequality for functions that take values in these algebras. Our extension faces significant hurdles due to the unique characteristics of the Cayley–Dickson Fourier transform. This transformation diverges from the classical Fourier transform in several key aspects: it does not conform to the Plancherel theorem, alters the interplay between derivatives and multiplication, and the product of algebra elements does not necessarily maintain the magnitude relationships found in classical settings. To overcome these challenges, our approach involves constructing the Cayley–Dickson Fourier transform by sequentially applying classical Fourier transforms. A pivotal part of our strategy is the utilization of a theorem that facilitates the norm-preserving extension of linear operators between spaces <span>(L^p)</span> and <span>(L^q.)</span> Furthermore, our investigation brings new insights into the complexities surrounding the Beckner–Hirschman Entropic inequality in the context of non-associative algebras.</p></div>","PeriodicalId":7330,"journal":{"name":"Advances in Applied Clifford Algebras","volume":"34 3","pages":""},"PeriodicalIF":1.1,"publicationDate":"2024-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140903199","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Machine Learning Clifford Invariants of ADE Coxeter Elements","authors":"Siqi Chen, Pierre-Philippe Dechant, Yang-Hui He, Elli Heyes, Edward Hirst, Dmitrii Riabchenko","doi":"10.1007/s00006-024-01325-y","DOIUrl":"10.1007/s00006-024-01325-y","url":null,"abstract":"<div><p>There has been recent interest in novel Clifford geometric invariants of linear transformations. This motivates the investigation of such invariants for a certain type of geometric transformation of interest in the context of root systems, reflection groups, Lie groups and Lie algebras: the Coxeter transformations. We perform exhaustive calculations of all Coxeter transformations for <span>(A_8)</span>, <span>(D_8)</span> and <span>(E_8)</span> for a choice of basis of simple roots and compute their invariants, using high-performance computing. This computational algebra paradigm generates a dataset that can then be mined using techniques from data science such as supervised and unsupervised machine learning. In this paper we focus on neural network classification and principal component analysis. Since the output—the invariants—is fully determined by the choice of simple roots and the permutation order of the corresponding reflections in the Coxeter element, we expect huge degeneracy in the mapping. This provides the perfect setup for machine learning, and indeed we see that the datasets can be machine learned to very high accuracy. This paper is a pump-priming study in experimental mathematics using Clifford algebras, showing that such Clifford algebraic datasets are amenable to machine learning, and shedding light on relationships between these novel and other well-known geometric invariants and also giving rise to analytic results.</p></div>","PeriodicalId":7330,"journal":{"name":"Advances in Applied Clifford Algebras","volume":"34 3","pages":""},"PeriodicalIF":1.1,"publicationDate":"2024-05-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00006-024-01325-y.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140845242","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Exploring Quaternion Neural Network Loss Surfaces","authors":"Jeremiah Bill, Bruce Cox","doi":"10.1007/s00006-024-01313-2","DOIUrl":"10.1007/s00006-024-01313-2","url":null,"abstract":"<div><p>This paper explores the superior performance of quaternion multi-layer perceptron (QMLP) neural networks over real-valued multi-layer perceptron (MLP) neural networks, a phenomenon that has been empirically observed but not thoroughly investigated. The study utilizes loss surface visualization and projection techniques to examine quaternion-based optimization loss surfaces for the first time. The primary contribution of this research is the statistical evidence that QMLP models yield smoother loss surfaces than real-valued neural networks, which are measured and compared using a robust quantitative measure of loss surface “goodness” based on estimates of surface curvature. Extensive computational testing validates the effectiveness of these surface curvature estimates. The paper presents a comprehensive comparison of the average surface curvature of a tuned QMLP model and a tuned real-valued MLP model on both a regression task and a classification task. The results provide strong support for the improved optimization performance observed in QMLPs across various problem domains.</p></div>","PeriodicalId":7330,"journal":{"name":"Advances in Applied Clifford Algebras","volume":"34 3","pages":""},"PeriodicalIF":1.1,"publicationDate":"2024-04-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00006-024-01313-2.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140640399","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Fractional Elliptic Operators with Multiple Poles on Riemannian Manifold with Clifford Bundle","authors":"Rami Ahmad El-Nabulsi, Waranont Anukool","doi":"10.1007/s00006-024-01318-x","DOIUrl":"10.1007/s00006-024-01318-x","url":null,"abstract":"<div><p>We introduce new types of fractional generalized elliptic operators on a compact Riemannian manifold with Clifford bundle. The theory is applicable in well-defined differential geometry. The Connes-Moscovici theorem gives rise to dimension spectrum in terms of residues of zeta functions, applicable in the presence of multiple poles. We have discussed the problem of scalar fields over the unit co-sphere on the cotangent bundle and we have evaluated the associated Dixmier traces as Wodzicki residues. It was observed the emergence of different types of elliptic operators, including inverse square, fractional and higher-order operators which are practical in various fields including cyclic cohomology and index problems in theoretical physics.</p></div>","PeriodicalId":7330,"journal":{"name":"Advances in Applied Clifford Algebras","volume":"34 3","pages":""},"PeriodicalIF":1.1,"publicationDate":"2024-04-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140640424","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Multidimensional Generalized Fractional ({pmb {S}}) Transform","authors":"Lakshmanan Subbiah, Roopkumar Rajakumar","doi":"10.1007/s00006-024-01317-y","DOIUrl":"10.1007/s00006-024-01317-y","url":null,"abstract":"<div><p>In this paper, we introduce a new multidimensional fractional <i>S</i> transform <span>(S_{phi ,varvec{alpha },lambda })</span> using a generalized fractional convolution <span>(star _{varvec{alpha },lambda })</span> and a general window function <span>(phi )</span> satisfying some admissibility condition. The value of <span>(S_{phi ,varvec{alpha },lambda }f)</span> is also written in the form of inner product of the input function <i>f</i> with a suitable function <span>(phi _{textbf{t},textbf{u}}^{varvec{alpha }_{lambda }})</span>. The representation of <span>(S_{phi ,varvec{alpha },lambda }f)</span> in terms of the generalized fractional convolution helps us to obtain the Parseval’s formula for <span>(S_{phi ,varvec{alpha },lambda })</span> using the generalized fractional convolution theorem. Then, the inversion theorem is proved as a consequence of the Parseval’s identity. Using a generalized window function in the kernel of <span>(S_{phi ,varvec{alpha },lambda })</span> gives option to choose window function whose Fourier transform as a compactly supported smooth function or a rapidly decreasing function. We also discuss about the characterization of range of <span>(S_{phi ,varvec{alpha },lambda })</span> on <span>(L^2(mathbb {R}^N, mathbb {C}))</span>. Finally, we extend the transform to a class of quaternion valued functions consistently.</p></div>","PeriodicalId":7330,"journal":{"name":"Advances in Applied Clifford Algebras","volume":"34 3","pages":""},"PeriodicalIF":1.1,"publicationDate":"2024-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140603899","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"A Note on Cohomology of Clifford Algebras","authors":"Bikram Banerjee, Goutam Mukherjee","doi":"10.1007/s00006-024-01324-z","DOIUrl":"10.1007/s00006-024-01324-z","url":null,"abstract":"<div><p>In this article we construct a cochain complex of a complex Clifford algebra with coefficients in itself in a combinatorial fashion and we call the corresponding cohomology by <i>Clifford cohomology.</i> We show that <i>Clifford cohomology</i> controls the deformation of a complex Clifford algebra and can classify them up to Morita equivalence. We also study Hochschild cohomology groups and formal deformations of the algebra of smooth sections of a complex Clifford algebra bundle over an even dimensional orientable Riemannian manifold <i>M</i> which admits a <span>(Spin^{c})</span> structure.</p></div>","PeriodicalId":7330,"journal":{"name":"Advances in Applied Clifford Algebras","volume":"34 3","pages":""},"PeriodicalIF":1.1,"publicationDate":"2024-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140538358","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}