TY - JOUR AU - Tarcsay, Zsigmond AU - Sebestyén, Zoltán TI - Reduction of positive self-adjoint extensions JF - OPUSCULA MATHEMATICA J2 - OPUSC MATHEMATICA VL - 44 PY - 2024 IS - 3 SP - 425 EP - 438 PG - 14 SN - 1232-9274 DO - 10.7494/OpMath.2024.44.3.425 UR - https://m2.mtmt.hu/api/publication/34751048 ID - 34751048 N1 - Zsigmond Tarcsay was supported by the János Bolyai Research Scholarship of the Hungarian Academy of Sciences, and by the ÚNKP–22-5-ELTE-1096 New National Excellence Program of the Ministry for Innovation and Technology. LA - English DB - MTMT ER - TY - JOUR AU - Sebestyén, Zoltán AU - Tarcsay, Zsigmond TI - Extensions of positive symmetric operators and Krein's uniqueness criteria JF - LINEAR AND MULTILINEAR ALGEBRA J2 - LINEAR MULTILINEAR A PY - 2023 SN - 0308-1087 DO - 10.1080/03081087.2023.2196610 UR - https://m2.mtmt.hu/api/publication/33766588 ID - 33766588 N1 - Export Date: 11 September 2023 Correspondence Address: Tarcsay, Z.; Department of Applied Analysis and Computational Mathematics, Pázmány Péter sétány 1/c, Hungary; email: zsigmond.tarcsay@ttk.elte.hu LA - English DB - MTMT ER - TY - JOUR AU - Sebestyén, Zoltán AU - Tarcsay, Zsigmond TI - On the Krein-von Neumann and Friedrichs extension of positive operators JF - ACTA WASAENSIA J2 - ACTA WASA VL - 462 PY - 2021 SP - 165 EP - 178 PG - 14 SN - 0355-2667 UR - https://m2.mtmt.hu/api/publication/32080890 ID - 32080890 LA - English DB - MTMT ER - TY - JOUR AU - Tarcsay, Zsigmond AU - Sebestyén, Zoltán TI - Canonical Graph Contractions of Linear Relations on Hilbert Spaces JF - COMPLEX ANALYSIS AND OPERATOR THEORY J2 - COMPLEX ANAL OPER TH VL - 15 PY - 2021 IS - 1 SN - 1661-8254 DO - 10.1007/s11785-020-01066-3 UR - https://m2.mtmt.hu/api/publication/31840162 ID - 31840162 N1 - Export Date: 7 September 2022 Correspondence Address: Tarcsay, Z.; Department of Applied Analysis and Computational Mathematics, Pázmány Péter sétány 1/c, Hungary; email: tarcsay@cs.elte.hu LA - English DB - MTMT ER - TY - JOUR AU - Tarcsay, Zsigmond AU - Sebestyén, Zoltán TI - Range-kernel characterizations of operators which are adjoint of each other JF - ADVANCES IN OPERATOR THEORY J2 - ADV OPERAT THEORY VL - 5 PY - 2020 IS - 3 SP - 1026 EP - 1038 PG - 13 SN - 2538-225X DO - 10.1007/s43036-020-00068-4 UR - https://m2.mtmt.hu/api/publication/31300976 ID - 31300976 N1 - Cited By :3 Export Date: 7 September 2022 Correspondence Address: Tarcsay, Z.; Department of Applied Analysis and Computational Mathematics, Pázmány Péter sétány 1/c., Hungary; email: tarcsay@cs.elte.hu LA - English DB - MTMT ER - TY - JOUR AU - Sebestyén, Zoltán AU - Tarcsay, Zsigmond TI - On the adjoint of Hilbert space operators JF - LINEAR AND MULTILINEAR ALGEBRA J2 - LINEAR MULTILINEAR A VL - 67 PY - 2019 IS - 3 SP - 625 EP - 645 PG - 21 SN - 0308-1087 DO - 10.1080/03081087.2018.1430120 UR - https://m2.mtmt.hu/api/publication/30446535 ID - 30446535 N1 - Funding Agency and Grant Number: Hungarian Ministry of Human Capacities [NTP-NFTO-17] Funding text: Zsigmond Tarcsay was supported by the Hungarian Ministry of Human Capacities [grant number NTP-NFTO-17]. AB - In general, it is a non-trivial task to determine the adjoint S* of an unbounded operator S acting between two Hilbert spaces. We provide necessary and sufficient conditions for a given operator T to be identical with S*. In our considerations, a central role is played by the operator matrix M-S,M-T = (I -T S I). Our approach has several consequences such as characterizations of closed, normal, skew- and selfadjoint, unitary and orthogonal projection operators in real or complex Hilbert spaces. We also give a self-contained proof of the fact that T*T always has a positive selfadjoint extension. LA - English DB - MTMT ER - TY - JOUR AU - Sebestyén, Zoltán AU - Tarcsay, Zsigmond AU - Titkos, Tamás TI - A characterization of positive normal functionals on the full operator algebra JF - OPERATOR THEORY: ADVANCES AND APPLICATIONS J2 - OPER THER ADV APPL VL - 268 PY - 2018 SP - 443 EP - 447 PG - 5 SN - 0255-0156 DO - 10.1007/978-3-319-75996-8_24 UR - https://m2.mtmt.hu/api/publication/30789347 ID - 30789347 N1 - Export Date: 5 September 2019 Correspondence Address: Sebestyén, Z.; Department of Applied Analysis, Eötvös Loránd University, Pázmány Péter sétány 1/c, Hungary; email: sebesty@cs.elte.hu Funding text 1: Zsigmond Tarcsay was supported by the Hungarian Ministry of Human Capacities, NTP-NFTÖ-17. Corresponding author: Tamás Titkos. WoS:hiba:000787686500024 2022-12-21 12:34 típus nem egyezik AB - Using the recent theory of Krein-von Neumann extensions for positive functionals we present several simple criteria to decide whether a given positive functional on the full operator algebra B(H) is normal. We also characterize those functionals defined on the left ideal of finite rank operators that have a normal extension. © 2018, Springer International Publishing AG, part of Springer Nature. LA - English DB - MTMT ER - TY - JOUR AU - Hassi, S. AU - Sebestyén, Zoltán AU - De, Snoo H. TI - Lebesgue type decompositions for linear relations and Ando's uniqueness criterion JF - ACTA SCIENTIARUM MATHEMATICARUM (SZEGED) J2 - ACTA SCI MATH (SZEGED) VL - 84 PY - 2018 IS - 3-4 SP - 465 EP - 507 PG - 43 SN - 0001-6969 DO - 10.14232/actasm-018-757-0 UR - https://m2.mtmt.hu/api/publication/30349889 ID - 30349889 N1 - Export Date: 17 December 2018 Export Date: 2 January 2019 Funding details: Agricultural Marketing Service, 2010 Funding details: Suomalainen Tiedeakatemia Funding text 1: Received January 11, 2018 and in final form April 30, 2018. AMS Subject Classification (2010): 4705, 47A06, 47A65; 46N30, 47N30. Key words and phrases: regular relations, singular relations, (weak) Lebesgue type decompositions, uniqueness of decompositions, domination of relations and operators, closability. The research was partially supported by a grant from the Vilho, Yrjö and Kalle Väisälä Foundation of the Finnish Academy of Science and Letters. Funding Agency and Grant Number: Vilho, Yrjo and Kalle Vaisala Foundation of the Finnish Academy of Science and Letters Funding text: The research was partially supported by a grant from the Vilho, Yrjo and Kalle Vaisala Foundation of the Finnish Academy of Science and Letters. Export Date: 5 September 2019 Funding details: Utah Academy of Sciences, Arts and Letters Funding text 1: Received January 11, 2018 and in final form April 30, 2018. AMS Subject Classification (2010): 4705, 47A06, 47A65; 46N30, 47N30. Key words and phrases: regular relations, singular relations, (weak) Lebesgue type decompositions, uniqueness of decompositions, domination of relations and operators, closability. The research was partially supported by a grant from the Vilho, Yrjö and Kalle Väisälä Foundation of the Finnish Academy of Science and Letters. LA - English DB - MTMT ER - TY - JOUR AU - Sebestyén, Zoltán AU - Tarcsay, Zsigmond TI - On the square root of a positive selfadjoint operator JF - PERIODICA MATHEMATICA HUNGARICA J2 - PERIOD MATH HUNG VL - 75 PY - 2017 IS - 2 SP - 268 EP - 272 PG - 5 SN - 0031-5303 DO - 10.1007/s10998-017-0192-1 UR - https://m2.mtmt.hu/api/publication/3293570 ID - 3293570 N1 - Cited By :7 Export Date: 7 September 2022 Correspondence Address: Tarcsay, Z.; Department of Applied Analysis, Pázmány Péter sétány 1/c, Hungary; email: tarcsay@cs.elte.hu AB - We provide a short, elementary proof of the existence and uniqueness of the square root in the context of unbounded positive selfadjoint operators on real or complex Hilbert spaces. LA - English DB - MTMT ER - TY - JOUR AU - Sebestyén, Zoltán AU - Tarcsay, Zsigmond TI - Adjoint of sums and products of operators in Hilbert spaces JF - ACTA SCIENTIARUM MATHEMATICARUM (SZEGED) J2 - ACTA SCI MATH (SZEGED) VL - 82 PY - 2016 IS - 1-2 SP - 175 EP - 191 PG - 17 SN - 0001-6969 DO - 10.14232/actasm-015-809-3 UR - https://m2.mtmt.hu/api/publication/3084669 ID - 3084669 N1 - Cited By :11 Export Date: 7 September 2022 LA - English DB - MTMT ER -