A collection of survey papers on the 50th anniversary of the institute.

The Sixth International Workshop on Complex Structures and Vector Fields was a continuation of the previous five workshops (1992, 1994, 1996, 1998, 2000) on similar research projects. This series of workshops aims at higher achievements in studies of new research subjects. The present volume will meet with the satisfaction of many readers.

The book incorporates research papers and surveys written by participants ofan International Scientific Programme on Approximation Theory jointly supervised by Institute for Constructive Mathematics of University of South Florida at Tampa, USA and the Euler International Mathematical Instituteat St. Petersburg, Russia. The aim of the Programme was to present new developments in Constructive Approximation Theory. The topics of the papers are: asymptotic behaviour of orthogonal polynomials, rational approximation of classical functions, quadrature formulas, theory of n-widths, nonlinear approximation in Hardy algebras,numerical results on best polynomial approximations, wavelet analysis. FROM THE CONTENTS: E.A. Rakhmanov: Strong asymptotics for orthogonal polynomials associated with exponential weights on R.- A.L. Levin, E.B. Saff: Exact Convergence Rates for Best Lp Rational Approximation to the Signum Function and for Optimal Quadrature in Hp.- H. Stahl: Uniform Rational Approximation of x .- M. Rahman, S.K. Suslov: Classical Biorthogonal Rational Functions.- V.P. Havin, A. Presa Sague: Approximation properties of harmonic vector fields and differential forms.- O.G. Parfenov: Extremal problems for Blaschke products and N-widths.- A.J. Carpenter, R.S. Varga: Some Numerical Results on Best Uniform Polynomial Approximation of x on 0,1 .- J.S. Geronimo: Polynomials Orthogonal on the Unit Circle with Random Recurrence Coefficients.- S. Khrushchev: Parameters of orthogonal polynomials.- V.N. Temlyakov: The universality of the Fibonacci cubature formulas.

A discrete model for Kähler magnetic fields on a complex hyperbolic space / T. Adachi -- Integrability condition on the boundary parameters of the asymmetric exclusion process and matrix product ansatz / B. Aneva -- Remarks on the double-complex Laplacian / L. Apostolova -- Generalizations of conjugate connections / O. Calin, H. Matsuzoe, J. Zhang -- Asymptotics of generalized value distribution for Herglotz functions / Y. T. Christodoulides -- Cyclic hyper-scalar systems / S. Dimiev, M. S. Marinov, Z. Zhelev -- Plane curves associated with integrable dynamical systems of the Frenet-Serret type / P. A. Djondjorov, V. M. Vassilev, I. M. Mladenov -- Relativistic strain and electromagnetic photon-like objects / S. Donev, M. Tashkova -- A construction of minimal surfaces in flat tori by swelling / N. Ejiri -- On NLS equations on BD.I symmetric spaces with constant boundary conditions / V. S. Gerdjikov, N. A. Kostov -- Orthogonal almost complex structures on S[symbol] x R[symbol] / H. Hashimoto, M. Ohashi -- Persistence of solutions for some integrable shallow water equations / D. Henry -- Some geometric properties and objects related to Bézier curves / M. J. Hristov -- Heisenberg relations in the general case / B. Z. Iliev -- Poisson structures of equations associated with groups of diffeomorphisms / R. I. Ivanov -- Hyperbolic Gauss maps and parallel surfaces in hyperbolic three-space / M. Kokubu -- On the lax pair for two and three wave interaction system / N. A. Kostov -- Mathematical outlook of fractals and chaos related to simple orthorhombic Ising-Onsager-Zhang lattices / J. Ławrynowicz, S. Marchiafava, M. Nowak-Kepczyk -- A characterization of Clifford minimal hypersurfaces of a sphere in terms of their geodesics / S. Maeda -- On the curvature properties of real time-like hypersurfaces of Kähler manifolds with Norden metric / M. Manev, M. Teofilova -- Some submanifolds of almost contact manifolds with Norden metric / G. Nakova -- A short note on the double-complex Laplace operator / P. Popivanov -- Monogenic, hypermonogenic and holomorphic Cliffordian functions - a survey / I. P. Ramadanoff -- On some classes of exact solutions of eikonal equation / Ł. T. Stepień -- Dirichlet property for tessellations of tiling-type 4 on a plane by congrent pentagons / Y. Takeo, T. Adachi -- Almost complex connections on almost complex manifolds with Norden metric / M. Teofilova -- Pseudo-boson coherent and Fock states / D. A. Trifonov -- New integrable equations of mKdV type / T. I. Valchev -- Integrable dynamical systems of the Frenet-Serret type / V. M. Vassilev, P. A. Djondjorov, I. M. Mladenov

For physics students interested in the mathematics they use, and for math students interested in seeing how some of the ideas of their discipline find realization in an applied setting. The presentation strikes a balance between formalism and application, between abstract and concrete. The interconnections among the various topics are clarified both by the use of vector spaces as a central unifying theme, recurring throughout the book, and by putting ideas into their historical context. Enough of the essential formalism is included to make the presentation self-contained.

Since the first volume of this work came out in Germany in 1937, this book, together with its first volume, has remained standard in the field. Courant and Hilbert's treatment restores the historically deep connections between physical intuition and mathematical development, providing the reader with a unified approach to mathematical physics. The present volume represents Richard Courant's final revision of 1961.

This book provides a new mathematical theory for the treatment of an ample series of spatial problems of electrodynamics, particle physics, quantum mechanics and elasticity theory. This technique proves to be as powerful for solving the spatial problems of mathematical physics as complex analysis is for solving planar problems. The main analytic tool of the book, a non-harmonic version of hypercomplex analysis recently developed by the authors, is presented in detail. There are given applications of this theory to the boundary value problems of electrodynamics and elasticity theory as well as to the problem of quark confinement. A new approach to the linearization of special classes of the self-duality equation is also considered. Detailed proofs are given throughout. The book contains an extensive bibliography on closely related topics. This book will be of particular interest to academic and professional specialists and students in mathematics and physics who are interested in integral representations for partial differential equations. The book is self-contained and could be used as a main reference for special course seminars on the subject.