Some forms of excluded middle for linear orders

The intersection of a linearly ordered set of total subrelations of a total relation with range 2 need not be total, constructively.     

Generalized solutions to a linear discontinuous differential equation

In this paper we construct generalized solutions (weak solutions) to a linear discontinuous differential equation which appears as mathematical model in mechanics and for which usual methods are not quite adequate. The result is applied to the equation of an elastic beam on a Winkler type of foundation.     

Canonical forms for linear systems

This paper considers canonical forms for the similarity action of Gl(n) on $\text{∑}{}_{\mathrm{n,m}}\text{={(A,B)∈}\text{C}{}^{\mathrm{n}}\text{·}{}^{\mathrm{n}}\text{×}\text{C}{}^{\mathrm{n}}\text{·}{}^{\mathrm{m}}\text{}}$:

$\text{Gl(n×∑}{}_{\mathrm{n,m}}\text{→∑}{}_{\mathrm{n,m}}$

,

$\text{(H,(A,B))?(HAH}{}^{-1}\text{,HB)}$

Those canonical forms are obtained as an application of a more general method to select canonical elements M_c in the orbits $\text{O}{}_{\mathrm{M}}$ of a matrix group G acting on a set of matrices $\text{M}\text{?}\text{C}{}^{\mathrm{l}}\text{·}{}^{\mathrm{p}}$. We define a total order (?) on $\text{C}{}^{\mathrm{l}}\text{·}{}^{\mathrm{p}}$, different from the lexicographic order ^l? [0^l?x ? x <0, but $\text{0?x≠0 for x∈}\text{R}\text{]}$ and consider normalized $\text{O}{}_{\mathrm{M}}$-elements with a minimal number of parameters:

$\text{min{}\text{M}\text{?}\text{∈}\text{O}{}_{\mathrm{M}}\text{:}\text{M}\text{?}\text{normalized}}$

It is shown that the row and column echelon forms, the Jordan canonical form, and “nice” control canonical forms for reachable (A,B)-pairs have a homogeneous interpretation as such (?)-minimal orbit elements. Moreover new canonical forms for the general action (?) are determined via this method.     

A Saint-Venant type principle for Dirichlet forms on discontinuous media

We consider certain families of Dirichlet forms of diffusion type that describe the variational behaviour of possibly highly nonhomogeneous and nonisotropic bodies and we prove a structural Harnack inequality and Saint Venant type energy decays for their local solution. Estimates for the Green functions are also considered.

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Sunto Si considerano certe famiglie di forme di Dirichlet di tipo diffusione che descrivono il comportamento di corpi fortemente non omogenei e non isotropi e si provano per le relative soluzione locali una diseguaglianza di Harnack strutturale e stime tipo Saint Venant della decrescita dell'energia. Si studiano inoltre stime per la funzione di Green.

     

First order linear partial differential equations with discontinuous coefficients

Summary Si dà un teorema di esistenza e di unicità di soluzione generalizzata per il problema di Cauchy relativo all'equazione . Le ipotesi fatte sui coefficienti a_i(t, x) permettono discontinuità di tipo molto generale, purchè sia soddisfatta una certa «condizione di trasversalità» tra le caratteristiche dell'equazione e le discontinuità del campo di vettori che le definisce.     

Galerkin method for linear parabolic equations with discontinuous solutions

Finite-element schemes are developed for solving a linear equation of parabolic type with a discontinuous solution in the space variable. Existence and uniqueness of the solution of the corresponding Cauchy problem is proved. Accuracy bounds are obtained for the finite-element scheme and the Crank-Nicholson scheme.Translated from Vychislitel'naya i Prikladnaya Matematika, No. 66, pp. 33–40, 1988.     

Locking-free adaptive discontinuous Galerkin FEM for linear elasticity problems

An adaptive discontinuous Galerkin finite element method for linear elasticity problems is presented. We develop an a posteriori error estimate and prove its robustness with respect to nearly incompressible materials (absence of volume locking). Furthermore, we present some numerical experiments which illustrate the performance of the scheme on adaptively refined meshes.

     

Local linear kernel estimation of the discontinuous regression function

We address the problems of estimating the discontinuous regression function and also its jump points. We propose a method in two steps: we first estimate the jumps and finally the regression function is estimated by an adapted version of a local linear smoother which makes use of the estimated jumps. The practical performance of the proposed method is evaluated by using simulation studies and an application to a real-life problem.     

Some results in discontinuous fields and wave propogation

We present various applications of recently developed techniques which are an interplay between the differential geometry and the theory of distributions. We apply them to the microlocal theory, derive the general order transport equations for the strength of wave fronts, obtain the values of the jumps of the general Nth-order derivatives of the harmonic functions across the potential layers, and present the explicit formulas for an arbitrary order derivative of functions of the radial distance r.     

Representation of numbers by linear forms

The paper contains new theorems concerning the Frobenius problem, belonging to additive number theory, and using continued fractions. Translated fromMatematicheskie Zametki, Vol. 68, No. 2, pp. 210–216, August, 2000.