• Nonlinear optimization over a Weighted Independence System 

      [OWP-2008-10] Lee, Jon; Onn, Shmuel; Weismantel, Robert (Mathematisches Forschungsinstitut Oberwolfach, 2008-03-14)
      We consider the problem of optimizing a nonlinear objective function over a weighted independence system presented by a linear-optimization oracle. We provide a polynomial-time algorithm that determines an r-best solution ...
    • A note on delta hedging in markets with jumps 

      [OWP-2011-23] Mijatović, Aleksandar; Urusov, Mikhail A. (Mathematisches Forschungsinstitut Oberwolfach, 2011-05-21)
      Modelling stock prices via jump processes is common in financial markets. In practice, to hedge a contingent claim one typically uses the so-called delta-hedging strategy. This strategy stems from the Black–Merton–Scholes ...
    • A note on k[z]-Automorphisms in Two Variables 

      [OWP-2008-17] Edo, Eric; Essen, Arno van den; Maubach, Stefan (Mathematisches Forschungsinstitut Oberwolfach, 2008)
      We prove that for a polynomial $f \in k[x, y, z]$ equivalent are: (1)$f$ is a $k[z]$-coordinate of $k[z][x,y]$, and (2) $k[x, y, z]/(f)\cong k^[2]$ and $f(x,y,a)$ is a coordinate in $k[x,y]$ for some $a \in k$. This solves ...
    • Numerical Invariants and Moduli Spaces for Line Arrangements 

      [OWP-2017-02] Dimca, Alexandru; Ibadula, Denis; Măcinic, Daniela Anca (Mathematisches Forschungsinstitut Oberwolfach, 2017-02-01)
      Using several numerical invariants, we study a partition of the space of line arrangements in the complex projective plane, given by the intersection lattice types. We offer also a new characterization of the free plane ...
    • Observability of systems with delay convoluted observation 

      [OWP-2014-10] Verriest, Erik I.; Ivanov, Anatoli F. (Mathematisches Forschungsinstitut Oberwolfach, 2014-05-13)
      This paper analyzes finite dimensional linear time-invariant systems with observation of a delay, where that delay satisfies a particular implicit relation with the state variables, rendering the entire problem nonlinear. ...
    • Obtaining Error-Minimizing Estimates and Universal Entry-Wise Error Bounds for Low-Rank Matrix Completion 

      [OWP-2013-12] Király, Franz J.; Theran, Louis (Mathematisches Forschungsinstitut Oberwolfach, 2013-06-10)
      We propose a general framework for reconstructing and denoising single entries of incomplete and noisy entries. We describe: effective algorithms for deciding if and entry can be reconstructed and, if so, for reconstructing ...
    • Octonion Polynomials with Values in a Subalgebra 

      [OWP-2020-21] Chapman, Adam (Mathematisches Forschungsinstitut Oberwolfach, 2020-10-22)
      In this paper, we prove that given an octonion algebra $A$ over a field $F$, a subring $E \subseteq F$ and an octonion $E$-algebra $R$ inside $A$, the set $S$ of polynomials $f(x) \in A[x]$ satisfying $f(R) \subseteq R$ ...
    • On a Cheeger Type Inequality in Cayley Graphs of Finite Groups 

      [OWP-2019-20] Biswas, Arindam (Mathematisches Forschungsinstitut Oberwolfach, 2019-07-22) - (7 July - 7 October 2017)
      Let $G$ be a finite group. It was remarked by Breuillard-Green-Guralnick-Tao that if the Cayley graph $C(G,S)$ is an expander graph and is non-bipartite then the spectrum of the adjacency operator $T$ is bounded away from ...
    • On a Group Functor Describing Invariants of Algebraic Surfaces 

      [OWP-2019-08] Dietrich, Heiko; Moravec, Primož (Mathematisches Forschungsinstitut Oberwolfach, 2019-03-01)
      Liedtke (2008) has introduced group functors $K$ and $\tilde K$, which are used in the context of describing certain invariants for complex algebraic surfaces. He proved that these functors are connected to the theory of ...
    • On an Effective Variation of Kronecker’s Approximation Theorem Avoiding Algebraic Sets 

      [OWP-2017-28] Fukshansky, Lenny; German, Oleg; Moshchevitin, Nikolay (Mathematisches Forschungsinstitut Oberwolfach, 2017-10-19)
      Let $\Lambda \subset \mathbb R^n$ be an algebraic lattice, coming from a projective module over the ring of integers of a number field $K$. Let $\mathcal Z \subset \mathbb R^n$ be the zero locus of a finite collection of ...
    • On Canonical Forms for Two-person Zero-sum Limit Average Payoff Stochastic Games 

      [OWP-2011-35] Boros, Endre; Elbassioni, Khaled; Gurvich, Vladimir; Makino, Kazuhisa (Mathematisches Forschungsinstitut Oberwolfach, 2011-05-29)
      We consider two-person zero-sum mean payoff undiscounted stochastic games. We give a sufficient condition for the existence of a saddle point in uniformly optimal stationary strategies. Namely, we obtain sufficient ...
    • On Co-Minimal Pairs in Abelian Groups 

      [OWP-2019-19] Biswas, Arindam; Saha, Jyoti Prakash (Mathematisches Forschungsinstitut Oberwolfach, 2019-07-09)
      A pair of non-empty subsets $(W,W')$ in an abelian group $G$ is a complement pair if $W+W'=G$. $W'$ is said to be minimal to $W$ if $W+(W'\setminus \{w'\}) \neq G, \forall \,w'\in W'$. In general, given an arbitrary subset ...
    • On commuting varieties of nilradicals of borel subalgebras of reductive lie algebras 

      [OWP-2012-14] Goodwin, Simon M.; Röhrle, Gerhard (Mathematisches Forschungsinstitut Oberwolfach, 2012-12-04)
      Let $G$ be a connected reductive algebraic group defined over an algebraically closed field $\mathbb{k}$ of characteristic zero. We consider the commuting variety $\mathcal{C}(\mathfrak{u})$ of the nilradical $\mathfrak{u}$ ...
    • On Concentrators and Related Approximation Constants 

      [OWP-2013-14] Bondarenko, A. V.; Prymak, A.; Radchenko, D. (Mathematisches Forschungsinstitut Oberwolfach, 2013-06-10)
      Pippenger ([Pip77]) showed the existence of (6m, 4m, 3m, 6)-concentrator for each positive integer m using a probabilistic method. We generalize his approach and prove existence of (6m, 4m, 3m, 5.05)-concentrator (which ...
    • On conjugacy of MASAs and the outer automorphism group of the Cuntz algebra 

      [OWP-2013-21] Conti, Roberto; Hong, Jeong Hee; Szymański, Wojciech (Mathematisches Forschungsinstitut Oberwolfach, 2013-10-29)
      We investigate the structure of the outer automorphism group of the Cuntz algebra and the closely related problem of conjugacy of MASAa in $\mathcal{O}_n$. In particular, we exhibit an uncountable family of MASAs, conjugate ...
    • On densities of lattice arrangements intersecting every i-dimensional affine subspace 

      [OWP-2016-08] González Merino, Bernardo; Henze, Matthias (Mathematisches Forschungsinstitut Oberwolfach, 2016-05-10)
      In 1978, Makai Jr. established a remarkable connection between the volume-product of a convex body, its maximal lattice packing density and the minimal density of a lattice arrangement of its polar body intersecting every ...
    • On Generalizations of Kac-Moody Groups 

      [OWP-2010-06] Blok, Rieuwert J.; Hoffman, Corneliu (Mathematisches Forschungsinstitut Oberwolfach, 2010-03-10)
      In [7] we define a Curtis-Tits group as a certain generalization of a Kac-Moody group. We distinguish between orientable and non-orientable Curtis-Tits groups and identify all orientable Curtis-Tits groups as Kac-Moody ...
    • On Local Combinatorial Formulas for Chern Classes of Triangulated Circle Bundle 

      [OWP-2016-16] Mnev, Nikolai; Sharygin, Georgy (Mathematisches Forschungsinstitut Oberwolfach, 2016-08-17)
      Principal circle bundle over a PL polyhedron can be triangulated and thus obtains combinatorics. The triangulation is assembled from triangulated circle bundles over simplices. To every triangulated circle bundle over a ...
    • On periodic solutions and global dynamics in a periodic differential delay equation 

      [OWP-2014-08] Ivanov, Anatoli F.; Trofimchuk, Sergei I. (Mathematisches Forschungsinstitut Oberwolfach, 2014-05-13)
      Several aspects of global dynamics and the existence of periodic solutions are studied for the scalar differential delay equation $x'(t) = a(t)f(x([t-K]))$, where $f(x)$ is a continuous negative feedback function, $x \cdot ...
    • On Reflection Subgroups of Finite Coxeter Groups 

      [OWP-2011-06] Douglass, J. Matthew; Pfeiffer, Götz; Röhrle, Gerhard (Mathematisches Forschungsinstitut Oberwolfach, 2011-05-9)
      Let $W$ be a finite Coxeter group. We classify the reflection subgroups of $W$ up to conjugacy and give necessary and sufficient conditions for the map that assigns to a reflection subgroup $R$ of $W$ the conjugacy class ...