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Paradan’s wall crossing formula for partition functions and Khovanski-Pukhlikov differential operator

Arzu Boysal, Michèle Vergne (2009)

Annales de l’institut Fourier

Let P ( s ) be a family of rational polytopes parametrized by inequations. It is known that the volume of P ( s ) is a locally polynomial function of the parameters. Similarly, the number of integral points in P ( s ) is a locally quasi-polynomial function of the parameters. Paul-Émile Paradan proved a jump formula for this function, when crossing a wall. In this article, we give an algebraic proof of this formula. Furthermore, we give a residue formula for the jump, which enables us to compute it.

Paths of low weight in planar graphs

Igor Fabrici, Jochen Harant, Stanislav Jendrol' (2008)

Discussiones Mathematicae Graph Theory

The existence of paths of low degree sum of their vertices in planar graphs is investigated. The main results of the paper are: 1. Every 3-connected simple planar graph G that contains a k-path, a path on k vertices, also contains a k-path P such that for its weight (the sum of degrees of its vertices) in G it holds w G ( P ) : = ∑ u ∈ V ( P ) d e g G ( u ) ≤ ( 3 / 2 ) k ² + ( k ) 2. Every plane triangulation T that contains a k-path also contains a k-path P such that for its weight in T it holds w T ( P ) : = ∑ u ∈ V ( P ) d e g T ( u ) ≤ k ² + 13 k 3. Let G be a 3-connected simple planar graph of circumference...

Platonic hypermaps.

Breda d'Azevedo, Antonio J., Jones, Gareth A. (2001)

Beiträge zur Algebra und Geometrie

Polyhedral realisation of hyperbolic metrics with conical singularities on compact surfaces

François Fillastre (2007)

Annales de l’institut Fourier

A Fuchsian polyhedron in hyperbolic space is a polyhedral surface invariant under the action of a Fuchsian group of isometries (i.e. a group of isometries leaving globally invariant a totally geodesic surface, on which it acts cocompactly). The induced metric on a convex Fuchsian polyhedron is isometric to a hyperbolic metric with conical singularities of positive singular curvature on a compact surface of genus greater than one. We prove that these metrics are actually realised by exactly one convex...

Porozumění Dudeneyho přívěsku a dělení obrazců

Vlastimil Dlab (2016)

Pokroky matematiky, fyziky a astronomie

Článek se zabývá dělením rovinných mnohoúhelníků na konečný počet částí, z nichž lze sestavit jiné, předem zvolené mnohoúhelníky. Úvodní část je věnována historii těchto disekcí a důkazu Wallaceovy–Bolyaiovy–Gerwienovy věty, podle které lze mezi sebou transformovat libovolné dva mnohoúhelníky o stejném obsahu. Hlavním tématem článku je tzv. Dudeneyho přívěsek, tj. rozdělení rovnostranného trojúhelníku na čtyři části, z nichž lze složit čtverec. Dudeneyho konstrukce je i po sto letech od svého objevu...

Proč řešit graficky úlohy lineárního programování

Andrea Kubišová (2016)

Učitel matematiky

At universities focused on economy, Operation Research topics are usually included in the study plan, including solving of Linear Programming problems. A universal tool for their algebraic solution is (numerically difficult) Simplex Algorithm, for which it is necessary to know at least the fundamental of Matrix Algebra. To illustrate this method of solving LP problems and to discuss all types of results, it seems to be very convenient to include a chapter about graphic solutions to LP problems....

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