M. Belishev, S. Dobrokhotov, I. Ibragimov, A. P. Kiselev, S. Kislyakov, M. Lyalinov, Y. Matiyasevich, V. Romanov, V. Smyshlyaev, T. Suslina, N. Ural'tseva
On 13 June 2020 the prominent mathematician and expert in mechanics, head of the St. Petersburg school in the theory of diffraction and wave propagation Vasilii Mikhailovich Babich observed his 90th birthday. He is the author of many now classical results on the structure of high-frequency asymptotics of solutions of various problems in mathematical physics. The pioneering works in which he developed the ray method for elastic body and surface waves are particularly notable, as are his asymptotic constructions of localized solutions of linear partial differential equations, which have found many applications, and also a series of his papers justifying formulae for high-frequency asymptotics. Babich is an Honoured Scientist of the Russian Federation (2010). His achievements have been marked by the USSR State Prize, which he received together with A. S. Alekseev, V. S. Buldyrev, I. A. and L. A. Molotkov, G. I. Petrashen, and T.B. Yanovskaya for the development of the ray method (1982), the V.A. Fock prize of the Russian Academy of Sciences for the development of asymptotic methods in diffraction theory (1998), and the prize “A Life Devoted to Mathematics” of the Dynasty Foundation (2014). In previous issues of this journal there are tributes on the occasions of his 70th and 80th birthdays1 to Babich’s research, teaching, and organizational activities in science. A. P. Kiselev and V. P. Smyshlyaev analysed his role in the development of the St. Petersburg school of the theory of diffraction and wave propagation in the paper “The 70th birthday of V. M. Babich” (Zap. Nauchn. Sem. S.-Peterburg. Otdel. Mat. Inst. Steklov. (POMI) 275 (2001), 9–16).2 Babich continues to do fruitful research in mathematical physics; in particular, he works on the theory of complex interference waves [1], [2]. In recent years he
2020年6月13日,著名数学家和力学专家、圣彼得堡衍射和波传播理论学院院长瓦西里·米哈伊洛维奇·巴比奇庆祝了他的90岁生日。他是许多关于数学物理中各种问题解的高频渐近结构的经典结果的作者。在他的开创性工作中,他发展了弹性体和表面波的射线方法,他对线性偏微分方程的局部解的渐近构造,发现了许多应用,以及他的一系列证明高频渐近公式的论文,都特别值得注意。巴比奇是俄罗斯联邦荣誉科学家(2010年)。他的成就被苏联国家奖所标志,他与A. S. Alekseev, V. S. Buldyrev, I. A. Molotkov和L. A. Molotkov, G. I. Petrashen和T.B. Yanovskaya一起获得了射线方法的发展(1982年),俄罗斯科学院的V.A. Fock奖用于发展衍射理论的渐近方法(1998年),以及王朝基金会的“一生致力于数学”奖(2014年)。在本杂志的前几期中,在巴比奇70岁和80岁生日的时候,有对他在科学领域的研究、教学和组织活动的致敬。A. P. Kiselev和V. P. Smyshlyaev在论文“V. M. Babich的70岁生日”(Zap)中分析了他在圣彼得堡衍射和波传播理论学派发展中的作用。Nauchn。扫描电镜。S.-Peterburg。Otdel。斯特克洛夫博士。(pomi) 275 (2001), 9-16).2巴比奇继续在数学物理方面进行卓有成效的研究;特别是,他研究的是复杂干涉波[1]b[2]的理论。近年来,他
{"title":"Vasilii Mikhailovich Babich","authors":"M. Belishev, S. Dobrokhotov, I. Ibragimov, A. P. Kiselev, S. Kislyakov, M. Lyalinov, Y. Matiyasevich, V. Romanov, V. Smyshlyaev, T. Suslina, N. Ural'tseva","doi":"10.1070/RM9987","DOIUrl":"https://doi.org/10.1070/RM9987","url":null,"abstract":"On 13 June 2020 the prominent mathematician and expert in mechanics, head of the St. Petersburg school in the theory of diffraction and wave propagation Vasilii Mikhailovich Babich observed his 90th birthday. He is the author of many now classical results on the structure of high-frequency asymptotics of solutions of various problems in mathematical physics. The pioneering works in which he developed the ray method for elastic body and surface waves are particularly notable, as are his asymptotic constructions of localized solutions of linear partial differential equations, which have found many applications, and also a series of his papers justifying formulae for high-frequency asymptotics. Babich is an Honoured Scientist of the Russian Federation (2010). His achievements have been marked by the USSR State Prize, which he received together with A. S. Alekseev, V. S. Buldyrev, I. A. and L. A. Molotkov, G. I. Petrashen, and T.B. Yanovskaya for the development of the ray method (1982), the V.A. Fock prize of the Russian Academy of Sciences for the development of asymptotic methods in diffraction theory (1998), and the prize “A Life Devoted to Mathematics” of the Dynasty Foundation (2014). In previous issues of this journal there are tributes on the occasions of his 70th and 80th birthdays1 to Babich’s research, teaching, and organizational activities in science. A. P. Kiselev and V. P. Smyshlyaev analysed his role in the development of the St. Petersburg school of the theory of diffraction and wave propagation in the paper “The 70th birthday of V. M. Babich” (Zap. Nauchn. Sem. S.-Peterburg. Otdel. Mat. Inst. Steklov. (POMI) 275 (2001), 9–16).2 Babich continues to do fruitful research in mathematical physics; in particular, he works on the theory of complex interference waves [1], [2]. In recent years he","PeriodicalId":49582,"journal":{"name":"Russian Mathematical Surveys","volume":"76 1","pages":"193 - 194"},"PeriodicalIF":0.9,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"59005337","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
where σ1 is a positive measure with support supp σ1 on a compact set E ⊂ R and h ∈ H (E) is a holomorphic function on E. If h(z) = σ̂2(z), where σ2 is a positive measure with support supp σ2 ⊂ F , where F ⊂ R E is a compact set, then the pair of functions f1, f2 forms a Nikishin system (see [6], and also [7], [5], [10], and the bibliography therein). Let Qn,j , j = 0, 1, 2, be the Hermite–Padé polynomials of the first type for the collection [1, f1, f2] with multi-index n = (n − 1, n, n), which means that deg Qn,j ⩽ n and (Qn,0 + Qn,1f1 + Qn,2f2)(z) = O(z−2n−2), z →∞. (2) For an arbitrary polynomial Q ∈ C[z] 0, let
{"title":"Interpolation properties of Hermite–Padé polynomials","authors":"S. Suetin","doi":"10.1070/RM10000","DOIUrl":"https://doi.org/10.1070/RM10000","url":null,"abstract":"where σ1 is a positive measure with support supp σ1 on a compact set E ⊂ R and h ∈ H (E) is a holomorphic function on E. If h(z) = σ̂2(z), where σ2 is a positive measure with support supp σ2 ⊂ F , where F ⊂ R E is a compact set, then the pair of functions f1, f2 forms a Nikishin system (see [6], and also [7], [5], [10], and the bibliography therein). Let Qn,j , j = 0, 1, 2, be the Hermite–Padé polynomials of the first type for the collection [1, f1, f2] with multi-index n = (n − 1, n, n), which means that deg Qn,j ⩽ n and (Qn,0 + Qn,1f1 + Qn,2f2)(z) = O(z−2n−2), z →∞. (2) For an arbitrary polynomial Q ∈ C[z] 0, let","PeriodicalId":49582,"journal":{"name":"Russian Mathematical Surveys","volume":"76 1","pages":"543 - 545"},"PeriodicalIF":0.9,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"59011762","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Andryi Valer'evich Malyutin, E. Fominykh, E. Shumakova
{"title":"[IMG align=ABSMIDDLE alt=$ 3$]tex_rm_5298_img1[/IMG]-manifolds given by [IMG align=ABSMIDDLE alt=$ 4$]tex_rm_5298_img2[/IMG]-regular graphs with three Euler cycles","authors":"Andryi Valer'evich Malyutin, E. Fominykh, E. Shumakova","doi":"10.1070/rm10013","DOIUrl":"https://doi.org/10.1070/rm10013","url":null,"abstract":"","PeriodicalId":49582,"journal":{"name":"Russian Mathematical Surveys","volume":"1 1","pages":""},"PeriodicalIF":0.9,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"59012253","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This survey is devoted to integrable polynomial Hamiltonian systems associated with symmetric powers of plane algebraic curves. We focus our attention on the relations (discovered by the authors) between the Stäckel systems, Novikov’s equations for the th stationary Korteweg– de Vries hierarchy, the Dubrovin–Novikov coordinates on the universal bundle of Jacobians of hyperelliptic curves, and new systems obtained by considering the symmetric powers of curves when the power is not equal to the genus of the curve. Bibliography: 52 titles.
本文研究与平面代数曲线对称幂相关的可积多项式哈密顿系统。我们的重点是(作者发现的)Stäckel系统、平稳Korteweg - de Vries层次的Novikov方程、超椭圆曲线jacobian泛束上的Dubrovin-Novikov坐标,以及考虑曲线的对称幂不等于曲线的格时得到的新系统之间的关系。参考书目:52篇。
{"title":"Integrable polynomial Hamiltonian systems and symmetric powers of plane algebraic curves","authors":"V. Buchstaber, A. Mikhailov","doi":"10.1070/RM10007","DOIUrl":"https://doi.org/10.1070/RM10007","url":null,"abstract":"This survey is devoted to integrable polynomial Hamiltonian systems associated with symmetric powers of plane algebraic curves. We focus our attention on the relations (discovered by the authors) between the Stäckel systems, Novikov’s equations for the th stationary Korteweg– de Vries hierarchy, the Dubrovin–Novikov coordinates on the universal bundle of Jacobians of hyperelliptic curves, and new systems obtained by considering the symmetric powers of curves when the power is not equal to the genus of the curve. Bibliography: 52 titles.","PeriodicalId":49582,"journal":{"name":"Russian Mathematical Surveys","volume":"76 1","pages":"587 - 652"},"PeriodicalIF":0.9,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"59011815","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We review the integrability of the geodesic flow on a threefold admitting one of the three group geometries in Thurston’s sense. We focus on the case. The main examples are the quotients , where is a cofinite Fuchsian group. We show that the corresponding phase space contains two open regions with integrable and chaotic behaviour, with zero and positive topological entropy, respectively. As a concrete example we consider the case of the modular threefold with the modular group . In this case is known to be homeomorphic to the complement of a trefoil knot in a 3-sphere. Ghys proved the remarkable fact that the lift of a periodic geodesic on the modular surface to produces the same isotopy class of knots as that which appears in the chaotic version of the celebrated Lorenz system and was studied in detail by Birman and Williams. We show that these knots are replaced by trefoil knot cables in the integrable limit of the geodesic system on . Bibliography: 60 titles.
{"title":"Chaos and integrability in -geometry","authors":"A. Bolsinov, A. Veselov, Y. Ye","doi":"10.1070/RM10008","DOIUrl":"https://doi.org/10.1070/RM10008","url":null,"abstract":"We review the integrability of the geodesic flow on a threefold admitting one of the three group geometries in Thurston’s sense. We focus on the case. The main examples are the quotients , where is a cofinite Fuchsian group. We show that the corresponding phase space contains two open regions with integrable and chaotic behaviour, with zero and positive topological entropy, respectively. As a concrete example we consider the case of the modular threefold with the modular group . In this case is known to be homeomorphic to the complement of a trefoil knot in a 3-sphere. Ghys proved the remarkable fact that the lift of a periodic geodesic on the modular surface to produces the same isotopy class of knots as that which appears in the chaotic version of the celebrated Lorenz system and was studied in detail by Birman and Williams. We show that these knots are replaced by trefoil knot cables in the integrable limit of the geodesic system on . Bibliography: 60 titles.","PeriodicalId":49582,"journal":{"name":"Russian Mathematical Surveys","volume":"76 1","pages":"557 - 586"},"PeriodicalIF":0.9,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"59011883","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The purpose of the survey is to systematize a vast amount of information about the minimal model program for varieties with group actions. We discuss the basic methods of the theory and give sketches of the proofs of some principal results. Bibliography: 243 titles.
{"title":"Equivariant minimal model program","authors":"Yuri Prokhorov","doi":"10.1070/RM9990","DOIUrl":"https://doi.org/10.1070/RM9990","url":null,"abstract":"The purpose of the survey is to systematize a vast amount of information about the minimal model program for varieties with group actions. We discuss the basic methods of the theory and give sketches of the proofs of some principal results. Bibliography: 243 titles.","PeriodicalId":49582,"journal":{"name":"Russian Mathematical Surveys","volume":"112 1","pages":"461 - 542"},"PeriodicalIF":0.9,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"59005611","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Boris Yakovlevich Kazarnovskii, A. Khovanskii, A. Esterov
The practice of bringing together the concepts of ‘Newton polytopes’, ‘toric varieties’, ‘tropical geometry’, and ‘Gröbner bases’ has led to the formation of stable and mutually beneficial connections between algebraic geometry and convex geometry. This survey is devoted to the current state of the area of mathematics that describes the interaction and applications of these concepts. Bibliography: 68 titles.
{"title":"Newton polytopes and tropical geometry","authors":"Boris Yakovlevich Kazarnovskii, A. Khovanskii, A. Esterov","doi":"10.1070/RM9937","DOIUrl":"https://doi.org/10.1070/RM9937","url":null,"abstract":"The practice of bringing together the concepts of ‘Newton polytopes’, ‘toric varieties’, ‘tropical geometry’, and ‘Gröbner bases’ has led to the formation of stable and mutually beneficial connections between algebraic geometry and convex geometry. This survey is devoted to the current state of the area of mathematics that describes the interaction and applications of these concepts. Bibliography: 68 titles.","PeriodicalId":49582,"journal":{"name":"Russian Mathematical Surveys","volume":"76 1","pages":"91 - 175"},"PeriodicalIF":0.9,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"59005162","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper is devoted to the resolution of singularities of holomorphic vector fields and one-dimensional holomorphic foliations in dimension three, and it has two main objectives. First, within the general framework of one-dimensional foliations, we build upon and essentially complete the work of Cano, Roche, and Spivakovsky (2014). As a consequence, we obtain a general resolution theorem comparable to the resolution theorem of McQuillan–Panazzolo (2013) but proved by means of rather different methods. The other objective of this paper is to consider a special class of singularities of foliations containing, in particular, all the singularities of complete holomorphic vector fields on complex manifolds of dimension three. We then prove that a much sharper resolution theorem holds for this class of holomorphic foliations. This second result was the initial motivation for this paper. It relies on combining earlier resolution theorems for (general) foliations with some classical material on asymptotic expansions for solutions of differential equations. Bibliography: 34 titles.
{"title":"On the resolution of singularities of one-dimensional foliations on three-manifolds","authors":"J. Rebelo, H. Reis","doi":"10.1070/RM9993","DOIUrl":"https://doi.org/10.1070/RM9993","url":null,"abstract":"This paper is devoted to the resolution of singularities of holomorphic vector fields and one-dimensional holomorphic foliations in dimension three, and it has two main objectives. First, within the general framework of one-dimensional foliations, we build upon and essentially complete the work of Cano, Roche, and Spivakovsky (2014). As a consequence, we obtain a general resolution theorem comparable to the resolution theorem of McQuillan–Panazzolo (2013) but proved by means of rather different methods. The other objective of this paper is to consider a special class of singularities of foliations containing, in particular, all the singularities of complete holomorphic vector fields on complex manifolds of dimension three. We then prove that a much sharper resolution theorem holds for this class of holomorphic foliations. This second result was the initial motivation for this paper. It relies on combining earlier resolution theorems for (general) foliations with some classical material on asymptotic expansions for solutions of differential equations. Bibliography: 34 titles.","PeriodicalId":49582,"journal":{"name":"Russian Mathematical Surveys","volume":"76 1","pages":"291 - 355"},"PeriodicalIF":0.9,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"59005926","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In the framework of a new approach to the concept of local symmetry in arbitrary Delone sets we obtain new results for such sets without any restrictions. These results have important consequences for lattices and regular systems. A conjecture about the crystal kernel is stated, which generalises significantly the classical theorem on the non-existence of a five-fold symmetry in three-dimensional lattices. The following theorems related to the foundations of geometric crystallography are proved.
{"title":"Local groups in Delone sets: a conjecture and results","authors":"N. Dolbilin, M. Shtogrin","doi":"10.1070/RM10037","DOIUrl":"https://doi.org/10.1070/RM10037","url":null,"abstract":"In the framework of a new approach to the concept of local symmetry in arbitrary Delone sets we obtain new results for such sets without any restrictions. These results have important consequences for lattices and regular systems. A conjecture about the crystal kernel is stated, which generalises significantly the classical theorem on the non-existence of a five-fold symmetry in three-dimensional lattices. The following theorems related to the foundations of geometric crystallography are proved.","PeriodicalId":49582,"journal":{"name":"Russian Mathematical Surveys","volume":"76 1","pages":"1137 - 1139"},"PeriodicalIF":0.9,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"59012763","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Alexander Mikhailovich Gagonov, Олег Иванович Мохов
In this note the well-known important problem of a complete description of compatible diagonal metrics is solved. In 2000 (see [1] and [2]) Mokhov obtained a complete explicit description of pairs of compatible metrics for which all eigenvalues are distinct. In the case of distinct eigenvalues such a pair of metrics can be simultaneously diagonalized and, as shown in [1] and [2], it is compatible if and only if the Nijenhuis tensor of the affinor associated with this pair of metrics vanishes. This made it possible in [1] and [2] to describe all such compatible metrics explicitly. The general case of pairs of compatible diagonal metrics that have coincident eigenvalues has remained unexplored despite its importance for applications. This case is completely investigated in this work. The general case of describing all pairs of compatible metrics remains an open problem to date. Compatible metrics play an important role in the theory of integrable systems, the Hamiltonian and bi-Hamiltonian theory of systems of hydrodynamic type, integrable hierarchies, the theory of Frobenius manifolds and their generalizations, the theory of multidimensional Poisson brackets, differential geometry and mathematical physics (see [3]–[12] and the review paper [13]). The general notion of compatible metrics was introduced by Mokhov in [1] and [2], and was motivated by the study of the compatibility conditions for local and non-local Poisson structures of hydrodynamic type, the theory of which was developed by Dubrovin and Novikov ([14], local theory) and Mokhov and Ferapontov ([15] and [16], non-local theory) for the purposes of the theory of systems of hydrodynamic type. Recall that a pair of contravariant (Riemannian or pseudo-Riemannian) metrics g 1 (u) and g ij 2 (u) is called almost compatible [1], [2] if for any linear combination g λ1,λ2(u) = λ1g ij 1 (u) + λ2g ij 2 (u) of these metrics, where λ1 and λ2 are arbitrary constants, the same linear relation holds for the Christoffel symbols corresponding to these metrics (the compatibility condition for the Levi-Civita connections of these metrics): Γ λ1,λ2;k(u) = λ1Γ ij 1;k(u) + λ2Γ ij 2;k(u), where Γ λ1,λ2;k(u) = g is λ1,λ2 (u)Γjλ1,λ2;sk(u), Γ ij 1;k(u) = g is 1 (u)Γ j 1;sk(u), and Γ ij 2;k(u) = g 2 (u)Γ j 2;sk(u). A pair of almost compatible metrics g ij 1 (u) and g ij 2 (u) is called compatible [1], [2] if for any linear combination g λ1,λ2(u) = λ1g ij 1 (u) + λ2g ij 2 (u) of these metrics, where λ1 and λ2 are arbitrary constants, the same linear relation holds for the Riemann curvature tensors corresponding to these metrics (the compatibility condition for the curvatures of these metrics):
本文解决了相容对角度量的完备描述这一众所周知的重要问题。在2000年(见[1]和[2]),Mokhov获得了所有特征值不同的兼容度量对的完整显式描述。在特征值不同的情况下,这样一对度量可以同时对角化,如[1]和[2]所示,当且仅当与这对度量相关的仿射的Nijenhuis张量消失时,它是相容的。这使得在[1]和[2]中可以显式地描述所有这些兼容指标。具有相同特征值的兼容对角度量对的一般情况尽管在应用中具有重要意义,但仍未被探索。在这项工作中,对这个案件进行了彻底的调查。迄今为止,描述所有兼容度量对的一般情况仍然是一个开放的问题。相容度量在可积系统理论、流体动力型系统的哈密顿和双哈密顿理论、可积层次、Frobenius流形理论及其推广、多维泊松括号理论、微分几何和数学物理中起着重要的作用(参见[3]-[12]和综述论文[13])。相容度规的一般概念是由Mokhov在[1]和[2]中提出的,其动机是对水动力型局部和非局部泊松结构的相容条件的研究,其理论是由Dubrovin和Novikov([14],局部理论)和Mokhov和Ferapontov([15]和[16],非局部理论)为水动力型系统的理论而发展起来的。回想一下,一对逆变(黎曼或伪黎曼)度量g 1 (u)和g ij 2(u)被称为几乎相容的[1],[2],如果对于这些度量的任何线性组合g λ1,λ2(u) = λ1g ij 1 (u) + λ2g ij 2(u),其中λ1和λ2是任意常数,对应于这些度量的Christoffel符号也成立相同的线性关系(这些度量的Levi-Civita连接的相容条件):Γλ1,λ2;k (u) =λ1Γij 1; k (u) +λ2Γij 2; k (u),在Γλ1λ2;k (u) = g是λ1λ2 (u)Γjλ1,λ2;sk (u),Γij 1; k (u) = g 1 (u)Γj 1; sk (u)和Γij 2; k (u) = g 2 (u)Γj 2; sk (u)。一对几乎相容的度量g ij 1 (u)和g ij 2(u)被称为相容的[1],[2]如果对于这些度量的任何线性组合g λ1,λ2(u) = λ1g ij 1 (u) + λ2g ij 2(u),其中λ1和λ2是任意常数,对应于这些度量的黎曼曲率张量的线性关系成立(这些度量的曲率的相容条件):
{"title":"On compatible diagonal metrics","authors":"Alexander Mikhailovich Gagonov, Олег Иванович Мохов","doi":"10.1070/RM10031","DOIUrl":"https://doi.org/10.1070/RM10031","url":null,"abstract":"In this note the well-known important problem of a complete description of compatible diagonal metrics is solved. In 2000 (see [1] and [2]) Mokhov obtained a complete explicit description of pairs of compatible metrics for which all eigenvalues are distinct. In the case of distinct eigenvalues such a pair of metrics can be simultaneously diagonalized and, as shown in [1] and [2], it is compatible if and only if the Nijenhuis tensor of the affinor associated with this pair of metrics vanishes. This made it possible in [1] and [2] to describe all such compatible metrics explicitly. The general case of pairs of compatible diagonal metrics that have coincident eigenvalues has remained unexplored despite its importance for applications. This case is completely investigated in this work. The general case of describing all pairs of compatible metrics remains an open problem to date. Compatible metrics play an important role in the theory of integrable systems, the Hamiltonian and bi-Hamiltonian theory of systems of hydrodynamic type, integrable hierarchies, the theory of Frobenius manifolds and their generalizations, the theory of multidimensional Poisson brackets, differential geometry and mathematical physics (see [3]–[12] and the review paper [13]). The general notion of compatible metrics was introduced by Mokhov in [1] and [2], and was motivated by the study of the compatibility conditions for local and non-local Poisson structures of hydrodynamic type, the theory of which was developed by Dubrovin and Novikov ([14], local theory) and Mokhov and Ferapontov ([15] and [16], non-local theory) for the purposes of the theory of systems of hydrodynamic type. Recall that a pair of contravariant (Riemannian or pseudo-Riemannian) metrics g 1 (u) and g ij 2 (u) is called almost compatible [1], [2] if for any linear combination g λ1,λ2(u) = λ1g ij 1 (u) + λ2g ij 2 (u) of these metrics, where λ1 and λ2 are arbitrary constants, the same linear relation holds for the Christoffel symbols corresponding to these metrics (the compatibility condition for the Levi-Civita connections of these metrics): Γ λ1,λ2;k(u) = λ1Γ ij 1;k(u) + λ2Γ ij 2;k(u), where Γ λ1,λ2;k(u) = g is λ1,λ2 (u)Γjλ1,λ2;sk(u), Γ ij 1;k(u) = g is 1 (u)Γ j 1;sk(u), and Γ ij 2;k(u) = g 2 (u)Γ j 2;sk(u). A pair of almost compatible metrics g ij 1 (u) and g ij 2 (u) is called compatible [1], [2] if for any linear combination g λ1,λ2(u) = λ1g ij 1 (u) + λ2g ij 2 (u) of these metrics, where λ1 and λ2 are arbitrary constants, the same linear relation holds for the Riemann curvature tensors corresponding to these metrics (the compatibility condition for the curvatures of these metrics):","PeriodicalId":49582,"journal":{"name":"Russian Mathematical Surveys","volume":"76 1","pages":"1140 - 1142"},"PeriodicalIF":0.9,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"59012914","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}