I. ON THE BILINEAR CONVOLUTION OPERATOR AND YOUNG’S INEQUALITY
https://doi.org/10.34130/1992-2752_2025_3_4
Evgeny A. Pavlov — Crimean Engineering and Pedagogical University named after Fevzi Yakubov.
Evgeny A. Rybalkin — Crimean Engineering and Pedagogical University named after Fevzi Yakubov, rybalkin_e@mail.ru
Abstract. In this paper, we prove the continuity of a bilinear convolution operator defined on a Cartesian product of symmetric spaces, which, in particular, implies a strengthening of Young’s inequality and, under some additional conditions, a strengthening of the theorem of S. G. Krein, Yu. I. Petunin and E. M. Semenov. The proof is carried out without using the theory of linear operator interpolation.
Keywords: symmetric spaces, convolution operation, operator norm.
References
- Krein S. G., Petunin Yu. I., Semenov E. M. Interpolyatsiya lineynykh operatorov [Interpolation of linear operators]. Moscow: Nauka, 1978. 400 p. (In Russ.)
- Pavlov E. A., Furmenko A. I. On the boundedness of the integral convolution operator in a pair of classical Lebesgue spaces Lp, Lr. Vestnik Tomskogo gosudarstvennogo universiteta. Matematika i mekhanika [Tomsk State University Bulletin. Mathematics and Mechanics]. 2023. No 83. Pp. 52–58. (In Russ.)
- Peleshenko B. I. Sufficient conditions for boundedness of convolution operators in rearrangement-invariant spaces. Sibirskii Matematicheskii Zhurnal [Siberian Math. J.]. 2001. Vol. 42. No 3. Pp. 645–650. (In Russ.)
- Burenkov V. I., Tararykova T. V. An analog of Young’s inequality for convolutions of functions for general Morrey-type spaces. Trudy MIAN [Proceedings of the Steklov Institute of Mathematics]. 2016. Vol. 293. Pp. 113–132. (In Russ.)
- Yong R. M. Interpolation in a Classical Hilbert Space of Entire Functions. Trans. Amer. Math. Soc. 1974. Vol. 192. Pp. 97–114.
- Edvards R. Ryady Fur’ye v sovremennom izlozhenii : v 2 t. [Fourier series in a modern presentation : in 2 volumes]. Translated from English by T. P. Lukashenko, V. A. Skvortsova. Moscow: Publishing House of the World, 1985. Vol. 2. 399 p. (In Russ.)
- Zigmynd А. Trigonometricheskiye ryady : v 2 t. [Trigonometric series : in 2 volumes]. Translated from English by O. S. Ivasheva-Musatova; edited by N. K. Bari. Moscow: Publishing House of the World, 1965. Vol. 2. 537 p. (In Russ.)
- Tribel Х. Teoriya i interpolyatsii. Funktsional’nyye neravenstva. Differentsial’nyye operatory : per. s angl. [Theory and interpolation. Functional inequalities and Differential operators : translated from English]. Moscow: Publishing House of the World, 1980. 664 p. (In Russ.)
- Bourbaki N. Vektornoye integrirovaniye, mera Khaara, svortka i predstaveniya : per. s fr. [Vector integration, Haar measure, convolution and representation : trans. from French]. Moscow: Science, 1970. 320 p.(In Russ.)
- Hardy G. G., Littlewood D. E., Polia G. Neravenstva [Inequalities]. Moscow: Foreign Literature, 1962. 456 p. (In Russ.)
- Blozinski A. P. On a Convolution Theorem for L(p, q) Spaces. Trans. Amer. Math. Soc. 1972. Vol. 164. Pp. 255–265.
- Benedek A., Calderon A. P., Panzone R. Convolution operators on functions with values in a Banach space. Matematika [Mathematics]. Vol. 7. Issue 5. Pp. 121–132. (In Russ.)
- Boyd D. W. Indices of Function Spaces and Their Relationship to Interpolation. Canadian Journal of Mathematics. 1969. Vol. 21 (5). Pp. 1245–1254.
- O’Neil R. Convolution operators and L(p,q) spaces. Duke Mathematical Journal. 1963. Vol. 30. Pp. 129–142.
For citation: Pavlov E. A., Rybalkin E. A. On the bilinear convolution operator and Young’s inequality. Vestnik Syktyvkarskogo universiteta. Seriya 1: Matematika. Mekhanika. Informatika [Bulletin of Syktyvkar University. Series 1: Mathematics. Mechanics. Informatics], 2025, no 3 (56), pp. 4−15. (In Russ.) https://doi.org/10.34130/1992-2752_2025_3_4

II. DESCRIPTION OF THE MOVEMENTS OF THE EUCLIDEAN PLANE IN BARYCENTRIC COORDINATES
https://doi.org/10.34130/1992-2752_2025_3_16
Marina A. Stepanova — The Herzen State Pedagogical University of Russia,
ratkebug@yandex.ru
Ksenia S. Malinnikova — The Herzen State Pedagogical University of Russia,
ratkebug@yandex.ru
Abstract. The affine transformation of a plane in a barycentric coordinate system is given by a system of linear equations with a barycentric matrix of size 3 × 3, so that each affine transformation of the plane can be associated with a matrix from the barycentric group
B˜(3).
Keywords: affine space, Euclidean plane, affine transformation, motion, barycentric coordinates, barycentric matrix, transformation matrix.
References
- Berzhe M. Geometriya : per. s frants. [Geometry : translated from French]. Moscow: Publishing House of the World, 1984. Vol. 1. 560 p. (In Russ.)
- Kostrikin A. I., Manin A. I. Lineynaya algebra i geometriya. 2-ye izd. [Linear Algebra and Geometry. 2nd ed.]. Moscow: Nauka Gl. red. fiz.-mat. lit., 1986. 304 p. (In Russ.)
- Ponarin Ya. P. Basic metric problems of plane geometry in barycentric coordinates. Matematicheskiy vestnik pedvuzov Volgo-Vyatskogo regiona [Mathematical Bulletin of Pedagogical Universities of the Volga-Vyatka Region]. 2002. Vol. 4. Pp. 114–132. (In Russ.)
- Ponarin Ya. P. Elementarnaya geometriya. Treugol’niki i tetraedry [Elementary Geometry. Triangles and Tetrahedra]. Moscow: MCNMO, Vol. 3. 192 p. (In Russ.)
- Stepanova M. A. Barycentric coordinate system. Barycentric group. Sovremennyye problemy matematiki i matematicheskogo obrazovaniya: Gertsenovskiye chteniya, 77 : sbornik nauchnykh trudov Mezhdunarodnoy nauchnoy konferentsii, Sankt- Peterburg,
16–18 aprelya 2024 g. [Contemporary Problems of Mathematics and Mathematical Education: Herzen Readings, 77 : collection of Proceedings of the International Scientific Conference, St. Petersburg, April 16–18, 2024]. A. I. Herzen State Pedagogical University. 2024. Pp. 356–360. (In Russ.) - Stepanova M. A. Some subgroups of the barycentric group. Vestnik Syktyvkarskogo universiteta. Seriya 1: Matematika. Mehanika. Informatika [Bulletin of Syktyvkar University. Series 1: Mathematics. Mechanics. Computer Science]. 2025. No 1 (54). Pp. 4–17. (In Russ.)
- Malinnikova K. S., Stepanova M. A. Barycentric matrices and canonical barycentric coordinates in Euclidean space. Sovremennyye problemy matematiki i matematicheskogo obrazovaniya: Gertsenovskiye chteniya, 78 : sbornik nauchnykh trudov Mezhdunarodnoy nauchnoy konferentsii, Sankt- Peterburg, 15–18 aprelya 2025 g. [Contemporary Problems of Mathematics and Mathematical Education: Herzen
Readings, 78 : collection of Scientific Papers from the International Scientific Conference, St. Petersburg, April 15–18, 2025]. A. I. Herzen State Pedagogical University. 2025. Pp. 360–364. (In Russ.) - Stegancev E. V., Steganceva P. G. Classification of motions of a plane equipped with a barycentric coordinate system. Vestnik Khersonskogo natsional’nogo tekhnicheskogo universiteta [Bulletin of the Kherson National Technical University]. 2014. No 3 (50). Pp. 480– (In Russ.)
- Davis P. J. Circulant Matrices. New York: Wiley Publ., 1979. 304 p.
- Sovertkov P. I. Spravochnik po elementarnoy matematike : uchebnoye posobiye. 2-ye izd., ster. [Handbook of Elementary Mathematics : Study Guide. 2nd ed., reprinted]. Sankt-Peterburg: Lan‘, 2022. 404 p. (In Russ.)
For citation: Stepanova M. A., Malinnikova K. S. Description of the movements of the Euclidean plane in barycentric coordinates. Vestnik Syktyvkarskogo universiteta. Seriya 1: Matematika. Mekhanika. Informatika [Bulletin of Syktyvkar University. Series 1: Mathematics.
Mechanics. Informatics], 2025, no 3 (56), pp. 16−32. (In Russ.) https://doi.org/10.34130/1992-2752_2025_3_4

III. METHODS FOR EXTRACTING LEADING INDICATORS OF INVESTMENT ACTIVITY FROM UNSTRUCTURED TEXT DATA
https://doi.org/10.34130/1992-2752_2025_3_33
Olga A. Maltseva — Bank of Russia, maltseva.rs@yandex.ru
Irina V. Polyakova — Bank of Russia.
Petr V. Borkov — Bank of Russia.
Denis S. Grimalyuk — Pitirim Sorokin Syktyvkar State University.
Yulia A. Yushkova — Pitirim Sorokin Syktyvkar State University.
Evgenija N. Startseva — Pitirim Sorokin Syktyvkar State University.
Abstract. The aim of this study is to construct a leading index of investment activity in Russia, calculated by assessing news dynamics using natural language processing (NLP) and machine learning methods.
Keywords: NLP, LLM, text analysis, machine learning, investment activity, leading indicators, Bayesian analysis.
References
- Borkov P. V., Maltseva O. A., Polyakova I. V., Startseva E. N. Assessment of investment activity based on the news background. Vestnik Syktyvkarskogo universiteta. Ser. 1: Matematika. Mekhanika. Informatika [Bulletin of Syktyvkar University. Series 1: Mathematics. Mechanics. Computer Science]. 2024. No 4 (53). Pp. 4–20. DOI: 10.34130/1992-2752_2024_4_4. (In Russ.)
- Chloe Y., Davidson T. Large Language Models for Text Classification: From Zero-Shot Learning to Fine-Tuning [Electronic resource]. Available at: https://osf.io/preprints/socarxiv/sthwk_v2 (accessed: 10.04.2025).
- Zhang Ya., Wang M., Ren C. et all. Pushing The Limit of LLM Capacity for Text Classification [Electronic resource]. arXiv preprint. 2024. Available at: https://arxiv.org/abs/2402.07470 (accessed: 21.11.2024).
- Handlan A. Text Shocks and Monetary Surprises: Text Analysis of FOMC Statements with Machine Learning : PhD dissertation. University of Minnesota. Minnesota, 2021. Available at: https://conservancy.umn.edu/server/api/core/bitstreams/c2c0e904- c84f-4833-afa2-a8f09ad4587a/content (accessed: 10.09.2025).
- G´ati L., Handlan A. Monetary Communication Rules. ECB Working Paper Series. No 2759. December 2022. 47 p. DOI: 10.2866/911830.
- Ilias F., Garciga C., Mitchell J., Nguyen M. T. Regional Economic Sentiment: Constructing Quantitative Estimates from the Beige Book and Testing Their Ability to Forecast Recessions. Economic Commentary. Federal Reserve Bank of Cleveland. 2024. Vol. 2024–08. Pp. 1–8. DOI: 10.26509/frbc-ec-202408.
- Gascon C. S., Martorana J. The Beige Book and the Business Cycle: Using Beige Book Anecdotes to Construct Recession Probabilities. Federal Reserve Bank of St. Louis Working 2024. Paper 2024-037B. 32 p. DOI: 10.20955/wp.2024.037
- Baker S. R., Bloom N., Davis S. J. Measuring Economic Policy Uncertainty. Quarterly Journal of Economics. 2016. Vol. 131 (4). Pp. 1593–1636. DOI: 10.1093/qje/qjw/024.
- Cerda R., Silva A., Valente J. T. Economic Policy Uncertainty Indices for Chile. Economic Policy Uncertainty Working Paper. 2016. Available at: https://policyuncertainty.com/media/EPU_Chile.pdf (accessed: 10.09.2025).
- Zalla R. Economic Policy Uncertainty in Ireland. Atlantic Economic Journal. 2017. Vol. 45 (2). Pp. 267–271. DOI: 10.1007/s11293-017- 9536-8.
- Petrova D., Trunin P. Assessment of the level of uncertainty of economic policy. Den’gi i kredit [Money and credit]. 2023. No 82 (3). Pp. 48–61. (In Russ.)
- Yakovleva K. Assessment of economic activity based on text analysis. Den’gi i kredit [Money and credit]. 2018. No 77 (4). Pp. 26–41. DOI: 10.31477/rjmf.201804.26. (In Russ.)
- Kolyuzhnov D. V., Kolyuzhnov E. D., Lyakhnova M. V. Taking into account the information background in the DSGE model of the Russian economy with adaptive learning. Mir ekonomiki i upravleniya [World of Economics and Management]. 2023. Vol. 23 (4). Pp. 60–82. DOI: 10.25205/2542-0429-2023-23-4-60-82. (In Russ.)
- Polekhina A., Guseva A. How the Bank of Russia Is Perceived on Telegram Channels: Building an Index Using Machine Learning Methods. Den’gi i Kredit [Money and Finance]. 2025. Vol. 84. No 3. Pp. 28–62. (In Russ.)
- Matthew G., Kelly B., Taddy M. Text as Data. Journal of Economic Literature. 2019. 57 (3). Pp. 535–574. DOI: 10.1257/jel.20181020.
- Hassani H., Beneki C., Unger S. et al. Text Mining in Big Data Analytics. Big Data Cogn. Comput. Vol. 4. Issue 1. 34 p. DOI: 10.3390/bdcc4010001.
- Thorsrud L. A. Words are the New Numbers: A Newsy Coincident Index of the Business Cycle. Journal of Business & Economic Statistics. 38 (2). Pp. 393–409. DOI: 10.1080/07350015.2018.1506344.
- Ash El., Hansen S. Text Algorithms in Economics. Annual Review of Economics. 2023. Vol. 15. Pp. 659–688. DOI: 10.1146/annureveconomics-082222-074352.
- Barbaglia L., Consoli S., Manzan S. Forecasting with Economic News. Journal of Business & Economic Statistics. 2023. January. 41 (107). 46 p. DOI: 10.1080/07350015.2022.2060988.
- Kalamara E., Turrell A., Redl C. et al. Making text count: Economic forecasting using newspaper text. Journal of Applied Econometrics. 2022. 37 (5). Pp. 896–919. DOI: 10.1002/jae.2907.
- Devlin J., Chang M.-W., Lee K., Toutanova K. BERT: Pre-training of Deep Bidirectional Transformers for Language Understanding. Proceedings of the 2019 Conference of the North American Chapter of the Association for Computational Linguistics: Human Language Technologies. Vol. 1. Long and Short Papers. Minneapolis, Minnesota: Association for Computational Linguistics, Pp. 4171–4186. DOI: 10.18653/v1/N19-1423.
- Ash E., Hansen S. Text Algorithms in Economics. Annual Review of Economics. 2023. Vol. 15. Pp. 659–688. DOI: 10.1146/annureveconomics-082222-074352.
- Subakti A., Murfi H., Hariadi N. The performance of BERT as data representation of text clustering. Journal of Big Data. 2022. Vol. 9. No 1. P. 15. DOI: 10.1186/s40537-022-00564-9.
- Cervantes J., Garcia Lamont F., Rodr´ıguez Mazahua L., Lopez A. A comprehensive survey on support vector machine classification: Applications, challenges and trends. Neurocomputing. Vol. 408. Pp. 189–215. DOI: 10.1016/j.neucom.2019.10.118.
- Kitov V. V. Mashinnoye i glubokoye obucheniye : onlaynuchebnik [Machine and Deep Learning: online textbook]. Moscow: Faculty of Computational Mathematics and Cybernetics, Moscow State University named after M. V. Lomonosov. 2025.Available at:
https://deepmachinelearning.ru (accessed: 10.09.2025). (In Russ.) - ML Handbook : uchebnik po mashinnomu obucheniyu [ML Handbook : a textbook on machine learning]. Yandex School of Data Analysis (YSD). Moscow, 2025. Available at: https://education.yandex.ru/handbook/ml (accessed: 10.09.2025). (In Russ.)
For citation: Maltseva O. A., Polyakova I. V., Borkov P. V., Grimalyuk D. S., Yushkova Yu. A., Startseva E. N. Methods for extracting leading indicators of investment activity from unstructured text data. Vestnik Syktyvkarskogo universiteta. Seriya 1: Matematika. Mekhanika. Informatika [Bulletin of Syktyvkar University, Series 1: Mathematics. Mechanics. Informatics], 2025, no 3 (56), pp. 33−60. (In Russ.) https://doi.org/10.34130/1992-2752_2025_3_33

IV. ON THE MODEL OF INFINITE DECIMAL FRACTIONS FROM THE PERSPECTIVE OF THE AXIOMATIC CONSTRUCTION OF THE THEORY OF REAL NUMBERS
https://doi.org/10.34130/1992-2752_2025_3_61
Vladislav V. Sushkov — Pitirim Sorokin Syktyvkar State University, vvsu@mail.ru
Abstract. This article addresses the justification of the infinite decimal fractions model within the framework of the axiomatic approach to the theory of real numbers. The relevance of the research is determined by the fundamental importance of a rigorous foundation for models of the continuum.
Keywords: real numbers, axiomatic theory, infinite decimal fractions, continuum, nested intervals, arithmetic operations, mathematical foundations
References
- Hilbert D. Osnovaniya geometrii [Foundations of Geometry]. Moscow; Leningrad: Gostekhizdat, 1948. 491 p. (In Russ.)
- Dedekind R. Stetigkeit und irrationale Zahlen. Braunschweig: Vieweg, 31 p.
- Cantor G. Trudy po teorii mnozhestv [Works on Set Theory]. Moscow: Science, 1985. 430 p. (In Russ.)
- Weierstrass K. Mathematische Werke. Berlin: Mayer & M¨uller, 1895. Vol. 3. 271 p.
- Kolmogorov A. N. On the Foundation of the Theory of Real Numbers. Uspekhi matematicheskikh nauk [Advances in Mathematical Sciences]. 1946. Vol. 1. No 1. Pp. 217–219. (In Russ.)
- Kudryavtsev L. D. On Mathematics. Matematika v vysshem obrazovanii [Mathematics in Higher Education]. 2009. No 7. Pp. 9–20. (In Russ.)
- Vechtomov E. M., Chermykh V. V., Shirokov D. V. Methods of Teaching the System of Real Numbers. Vestnik Vyatskogo gosudarstvennogo gumanitarnogo universiteta [Bulletin of Vyatka State University of Humanities]. 2012. No 2–3. Pp. 57–68. (In Russ.)
- Rusakov A. A., Chubarikov V. N. On Two Approaches to the Foundation of Real Numbers. Matematika v vysshem obrazovanii [Mathematics in Higher Education]. 2006. No 4. Pp. 37–44. EDN TCYPOZ. (In Russ.)
- Sotnikova O. A., Chermnykh V. V. Peculiarities of studying determinants in the preparation of mathematics teachers. Psikhologiya obrazovaniya v polikul’turnom prostranstve [Psychology of education in a multicultural environment]. 2024. No 4 (68). Pp. 117–125. (In Russ.)
- Nikitin A. A., Fomichev V. V. Matematicheskiy analiz. Uglublennyy kurs : uchebnik i praktikum dlya vuzov [Mathematical Analysis. Advanced Course : textbook and Workshop for Universities]. 2nd ed., rev. and add. Moscow: Yurait, 2025. 456 p. (In Russ.)
For citation: Sushkov V. V. On the Model of Infinite Decimal Fractions from the Perspective of the Axiomatic Construction of the Real Number Theory. Vestnik Syktyvkarskogo universiteta. Seriya 1: Matematika. Mekhanika. Informatika [Bulletin of Syktyvkar University. Series 1: Mathematics. Mechanics. Informatics], 2025, no 3 (56), pp. 61−73. (In Russ.) https://doi.org/10.34130/1992-2752_2025_3_61

V. EFFICIENT SOLUTION OF THE BIHARMONIC EQUATION BASED ON SPARSE DATA STRUCTURES
https://doi.org/10.34130/1992-2752_2025_3_74
Andrei V. Yermolenko — Pitirim Sorokin Syktyvkar State University, ea74@list.ru
Lev S. Shadrin — Pitirim Sorokin Syktyvkar State University.
Abstract. This article presents a numerical solution to the biharmonic equation by reducing it to a system of linear algebraic equations. Two approaches are explored: the first is based on
approximating the biharmonic operator using a 13-point stencil, while the second is based on reducing the original problem to a system of two Poisson equations followed by discretization of the Laplace operator using a 5-point stencil.
Keywords: biharmonic equation, numerical methods, sparse matrices.
References
- Petrova G. N., Larionov S. A., Platonov M. M., Perfilova D. N. Thermoplastic materials of a new generation for aviation. Aviatsionnye materialy i tekhnologii [Aviation Materials and Technologies]. 2017. No S. Pp. 420–436. (In Russ.)
- Chemodurov V. T., Kuzmenko O. A. Influence of methods of fastening of a plate on its transverse vibrations under constant aerodynamic load. Metodologiya bezopasnosti sredy zhiznedeyatel’nosti : programma i tezisy IV Krymskoy Mezhdunarodnoy nauchnoprakticheskoy konferentsii, Simferopol’ — Sudak, 25–29 sentyabrya 2017 goda [Methodology of Environmental Safety of Human Environment : Program and Abstracts of the IV Crimean International Scientific and Practical Conference, Simferopol –– Sudak, September 25–29]. Edited by A. T. Dvoretsky, T. V. Denisova, A. E. Maksimenko. Simferopol; Sudak: Krymskii federalnyi universitet im. V. I. Vernadskogo, 2017. P. 77. EDN ZSVDXT. (In Russ.)
- Volmir A. S. Nelineynaya dinamika plastinok i obolochek [Nonlinear dynamics of plates and shells]. Moscow: Science, 1972. 432 p. (In Russ.)
- Yermolenko A. V. Kontaktnyye zadachi so svobodnoy granitsey [Contact problems with a free boundary]. Syktyvkar: Pitirim Sorokin Syktyvkar State University Press, 2020. 105 p. 1 optical disk (CDROM). (In Russ.)
- Yermolenko A. V., Kozhageldiev N. V. Numerical solution of an inhomogeneous biharmonic equation. Vestnik Syktyvkarskogo universiteta. Seriya 1: Matematika. Mekhanika. Informatika [Bulletin of Syktyvkar University. Series 1: Mathematics. Mechanics. Informatics]. No 3 (44). Pp. 64–78.
- Pissanetsky S. Tekhnologiya razrezhennykh matrits [Sparse matrix technology]. Moscow: Peace, 1988. 410 p. (In Russ.)
- Samarskii A. A. Vvedeniye v teoriyu raznostnykh skhem [Introduction to the theory of difference schemes]. Moscow: Science, 1971. 552 p. (In Russ.)
- Samarskii A. A., Gulin A. V. Chislennyye metody : ucheb. posobiye dlya vuzov [Numerical methods : a textbook for universities]. Moscow: Science. Main Editorial Board for Physical and Mathematical Literature, 1989. 432 p. (In Russ.)
- Yermolenko A. V., Osipov K. S. On using Python libraries to calculate plates. Vestnik Syktyvkarskogo universiteta. Seriya 1: Matematika. Mekhanika. Informatika [Bulletin of Syktyvkar University. Series 1: Mathematics. Mechanics. Informatics]. 2019. No 4 (33). Pp. 86– (In Russ.)
- SciPy: library for scientific computing in Python. [Electronic resource]. Available at: https://scipy.org (accessed: 11.08.2025).
For citation: Yermolenko A. V., Shadrin L. S. Efficient solution of the biharmonic equation based on sparse data structures. Vestnik Syktyvkarskogo universiteta. Seriya 1: Matematika. Mekhanika. Informatika [Bulletin of Syktyvkar University, Series 1: Mathematics. Mechanics. Informatics], 2025, no 3 (56), pp. 74−87. (In Russ.) https://doi.org/10.34130/1992-2752_2025_3_74
