Seppo Hassi

2.3k total citations
76 papers, 1.1k citations indexed

About

Seppo Hassi is a scholar working on Mathematical Physics, Computational Theory and Mathematics and Applied Mathematics. According to data from OpenAlex, Seppo Hassi has authored 76 papers receiving a total of 1.1k indexed citations (citations by other indexed papers that have themselves been cited), including 65 papers in Mathematical Physics, 50 papers in Computational Theory and Mathematics and 49 papers in Applied Mathematics. Recurrent topics in Seppo Hassi's work include Spectral Theory in Mathematical Physics (65 papers), Matrix Theory and Algorithms (39 papers) and Holomorphic and Operator Theory (34 papers). Seppo Hassi is often cited by papers focused on Spectral Theory in Mathematical Physics (65 papers), Matrix Theory and Algorithms (39 papers) and Holomorphic and Operator Theory (34 papers). Seppo Hassi collaborates with scholars based in Finland, Netherlands and United States. Seppo Hassi's co-authors include Henk de Snoo, H. S. V. de Snoo, M. M. Malamud, Jussi Behrndt, Henrik Winkler, Vladimir Derkach, Franciszek Hugon Szafraniec, Zoltán Sebestyén, Adrian Sandovici and Kenneth Nordström and has published in prestigious journals such as SHILAP Revista de lepidopterología, Journal of Mathematical Analysis and Applications and Transactions of the American Mathematical Society.

In The Last Decade

Seppo Hassi

72 papers receiving 1.1k citations

Peers — A (Enhanced Table)

Peers by citation overlap · career bar shows stage (early→late) cites · hero ref

Name h Career Trend Papers Cites
Seppo Hassi Finland 18 862 640 637 112 96 76 1.1k
Aad Dijksma Netherlands 17 623 0.7× 549 0.9× 464 0.7× 101 0.9× 86 0.9× 70 960
Henk de Snoo Netherlands 17 633 0.7× 447 0.7× 530 0.8× 83 0.7× 83 0.9× 54 805
Thomas Wolff United States 19 845 1.0× 1.0k 1.6× 334 0.5× 106 0.9× 113 1.2× 47 1.4k
Boris Mityagin United States 21 847 1.0× 484 0.8× 360 0.6× 68 0.6× 59 0.6× 66 1.1k
M. M. Malamud Ukraine 20 1.5k 1.7× 754 1.2× 947 1.5× 61 0.5× 25 0.3× 111 1.6k
Christiane Tretter Switzerland 17 665 0.8× 347 0.5× 546 0.9× 81 0.7× 38 0.4× 71 950
А. А. Шкаликов Russia 19 1.1k 1.2× 625 1.0× 708 1.1× 130 1.2× 17 0.2× 62 1.3k
Michael Solomyak Israel 20 931 1.1× 461 0.7× 550 0.9× 52 0.5× 17 0.2× 57 1.2k
Bernd Kirstein Germany 13 342 0.4× 514 0.8× 331 0.5× 53 0.5× 66 0.7× 97 733
L. Boutet de Monvel France 17 919 1.1× 938 1.5× 307 0.5× 91 0.8× 172 1.8× 44 1.5k

Countries citing papers authored by Seppo Hassi

Since Specialization
Citations

This map shows the geographic impact of Seppo Hassi's research. It shows the number of citations coming from papers published by authors working in each country. You can also color the map by specialization and compare the number of citations received by Seppo Hassi with the expected number of citations based on a country's size and research output (numbers larger than one mean the country cites Seppo Hassi more than expected).

Fields of papers citing papers by Seppo Hassi

Since Specialization
Physical SciencesHealth SciencesLife SciencesSocial Sciences

This network shows the impact of papers produced by Seppo Hassi. Nodes represent research fields, and links connect fields that are likely to share authors. Colored nodes show fields that tend to cite the papers produced by Seppo Hassi. The network helps show where Seppo Hassi may publish in the future.

Co-authorship network of co-authors of Seppo Hassi

This figure shows the co-authorship network connecting the top 25 collaborators of Seppo Hassi. A scholar is included among the top collaborators of Seppo Hassi based on the total number of citations received by their joint publications. Widths of edges represent the number of papers authors have co-authored together. Node borders signify the number of papers an author published with Seppo Hassi. Seppo Hassi is excluded from the visualization to improve readability, since they are connected to all nodes in the network.

All Works

20 of 20 papers shown
1.
Hassi, Seppo, et al.. (2025). Local Spectral Theory for Unbounded Product of Nonnegative Selfadjoint Operators. Complex Analysis and Operator Theory. 19(7).
2.
Hassi, Seppo & H. S. V. de Snoo. (2024). Sequences of Operators, Monotone in the Sense of Contractive Domination. Complex Analysis and Operator Theory. 18(4). 1 indexed citations
3.
Hassi, Seppo, et al.. (2024). Friedrichs and Kreĭn type extensions in terms of representing maps. Annals of Functional Analysis. 15(4). 1 indexed citations
4.
Derkach, Volodymyr, et al.. (2021). Unitary Boundary Pairs for Isometric Operators in Pontryagin Spaces and Generalized Coresolvents. Complex Analysis and Operator Theory. 15(2). 1 indexed citations
5.
Derkach, Volodymyr, Seppo Hassi, & M. M. Malamud. (2020). Generalized boundary triples, I. Some classes of isometric and unitary boundary pairs and realization problems for subclasses of Nevanlinna functions. Mathematische Nachrichten. 293(7). 1278–1327. 7 indexed citations
6.
Hassi, Seppo, Adrian Sandovici, H. S. V. de Snoo, & Henrik Winkler. (2017). Extremal maximal sectorial extensions of sectorial relations. Indagationes Mathematicae. 28(5). 1019–1055. 3 indexed citations
7.
Hassi, Seppo, H. S. V. de Snoo, & Franciszek Hugon Szafraniec. (2012). Infinite-dimensional perturbations, maximally nondensely defined symmetric operators, and some matrix representations. Indagationes Mathematicae. 23(4). 1087–1117. 6 indexed citations
8.
Hassi, Seppo, Zoltán Sebestyén, & Henk de Snoo. (2009). Lebesgue type decompositions for nonnegative forms. Journal of Functional Analysis. 257(12). 3858–3894. 30 indexed citations
9.
Behrndt, Jussi, Seppo Hassi, & Henk de Snoo. (2008). Functional models for Nevanlinna families. SHILAP Revista de lepidopterología. 8 indexed citations
10.
Hassi, Seppo, Adrian Sandovici, Henk de Snoo, & Henrik Winkler. (2007). A general factorization approach to the extension theory of nonnegative operators and relations. Journal of Operator Theory. 58(2). 351–386. 27 indexed citations
11.
Hassi, Seppo, et al.. (2006). Form Sums of Nonnegative Selfadjoint Operators. Acta Mathematica Academiae Scientiarum Hungaricae. 111(1). 81–105. 17 indexed citations
12.
Hassi, Seppo, et al.. (2006). A general realization theorem for matrix-valued Herglotz–Nevanlinna functions. Linear Algebra and its Applications. 419(2-3). 331–358. 5 indexed citations
13.
Hassi, Seppo, Manfred Möller, & Henk de Snoo. (2003). Sturm–Liouville operators and their spectral functions. Journal of Mathematical Analysis and Applications. 282(2). 584–602. 2 indexed citations
14.
Derkach, Vladimir & Seppo Hassi. (2003). A reproducing kernel space model for 𝐍_{𝜅}-functions. Proceedings of the American Mathematical Society. 131(12). 3795–3806. 7 indexed citations
15.
Hassi, Seppo, et al.. (2003). One-dimensional perturbations of selfadjoint operators with finite or discrete spectrum. Contemporary mathematics - American Mathematical Society. 419–433. 1 indexed citations
16.
Derkach, Vladimir, Seppo Hassi, & Henk de Snoo. (2002). SINGULAR PERTURBATIONS OF SELFADJOINT OPERATORS. Osuva (University of Vaasa). 2 indexed citations
17.
Derkach, Vladimir, Seppo Hassi, & Henk de Snoo. (2002). Rank One Perturbations in a Pontryagin Space with One Negative Square. Journal of Functional Analysis. 188(2). 317–349. 10 indexed citations
18.
Hassi, Seppo, et al.. (1998). Generalized Krein-von-Neumann extensions and associated operator models. Acta Scientiarum Mathematicarum. 687–715. 6 indexed citations
19.
Hassi, Seppo & Henk de Snoo. (1997). One-dimensional graph perturbations of selfadjoint relations. Annales Academiae Scientiarum Fennicae Mathematica. 22(1). 123–164. 27 indexed citations
20.
Hassi, Seppo & H. S. V. de Snoo. (1996). On some Subclasses of Nevanlinna Functions. Zeitschrift für Analysis und ihre Anwendungen. 15(1). 45–55. 6 indexed citations

Rankless uses publication and citation data sourced from OpenAlex, an open and comprehensive bibliographic database. While OpenAlex provides broad and valuable coverage of the global research landscape, it—like all bibliographic datasets—has inherent limitations. These include incomplete records, variations in author disambiguation, differences in journal indexing, and delays in data updates. As a result, some metrics and network relationships displayed in Rankless may not fully capture the entirety of a scholar's output or impact.

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