Essential Spectra and Essential Pseudospectra of a Linear Relations

Author(s):  
Aymen Ammar ◽  
Aref Jeribi
2018 ◽  
Vol 29 (7-8) ◽  
pp. 987-993 ◽  
Author(s):  
Aymen Ammar ◽  
Omar Jedidi ◽  
Aref Jeribi

2013 ◽  
Vol 37 (5) ◽  
pp. 620-644 ◽  
Author(s):  
Teresa Álvarez ◽  
Aymen Ammar ◽  
Aref Jeribi

2020 ◽  
Vol 2020 (1) ◽  
Author(s):  
Yan Liu ◽  
Meiru Xu

AbstractThis paper is concerned with stability of deficiency indices for discrete Hamiltonian systems under perturbations. By applying the perturbation theory of Hermitian linear relations we establish the invariance of deficiency indices for discrete Hamiltonian systems under bounded perturbations. As a consequence, we obtain the invariance of limit types for the systems under bounded perturbations. In particular, we build several criteria of the invariance of the limit circle and limit point cases for the systems. Some of these results improve and extend some previous results.


2021 ◽  
Author(s):  
Saskia Dönitz

AbstractThis article examines the content and structure of the manuscripts of Sefer Ḥasidim, engaging with ideas concerning its production addressed in Ivan Marcus’s recently published book on Sefer Ḥasidim. Marcus has argued that the book was written piece by piece and not as an integral book and further suggested that each and every manuscript of Sefer Ḥasidim should be taken as a distinct edition of the book prepared by Judah he-Ḥasid. The present study demonstrates that, notwithstanding the gradual process in which Sefer Ḥasidim was written and the great variations among the manuscripts, it is possible to reconstruct a textual process that led to the larger compilations found in the three well-known text editions of Sefer Ḥasidim, represented by MS Parma 3280, MS JTS Boesky 45, and the edition printed in Bologna in 1538. The analysis focuses on the distribution of the text in the manuscripts. While it is difficult to show linear relations among them, the different versions demonstrate a gradual process of growth and enlargement of the material around topical structures. Since most of the material is transmitted in more than one exemplar and few passages appear in one manuscript alone, it is argued that the manuscripts can be linked to show how the material grew from random collections of single paragraphs to topically ordered clusters and into the larger compilations of Sefer Ḥasidim.


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