Let f be an odd function of a class C2 such that ƒ(1) = 0,ƒ'(0) < 0,ƒ'(1) > 0 and $x\mapsto f(x)/x$ increases on [0,1]. We approximate the positive solution of Δu + ƒ(u) = 0, on $\xR_{+}^{2}$ with homogeneous Dirichlet boundary conditions by thesolution of $-\Delta u_{L}+f(u_{L})=0,$ on ]0,L[2 with adequatenon-homogeneous Dirichlet conditions. We show that the error uL - utends to zero exponentially fast, in the uniform norm.

A sparse algebraic multigrid method is studied as a cheap and accurateway to compute approximations of Schur complements of matricesarising from the discretization of some symmetric and positive definitepartial differential operators. The construction of such a multigrid isdiscussed and numerical experiments are used to verify the propertiesof the method.

The aim of this paper is to find estimates of the Green's function of stationary discrete shock profiles and discrete boundary layers of the modified Lax–Friedrichs numerical scheme, by using techniques developed by Zumbrun and Howard [CITE] in the continuous viscous setting.

We establish an asymptotic representation formula for the steady state voltageperturbations caused by low volume fraction internal conductivityinhomogeneities. This formula generalizes and unifies earlierformulas derived for special geometries and distributions of inhomogeneities.

In this paper we introduce numerical schemes for aone-dimensional kinetic model of the Boltzmann equation withdissipative collisions and variable coefficient of restitution. Inparticular, we study the numerical passage of the Boltzmannequation with singular kernel to nonlinear friction equations inthe so-called quasi elastic limit. To this aim we introduce aFourier spectral method for the Boltzmann equation [CITE]and show that the kernel modes that define the spectral methodhave the correct quasi elastic limit providing a consistentspectral method for the limiting nonlinear friction equation.

Domain decomposition techniques provide a powerful tool for the numerical approximation of partial differential equations.We focus on mortar finite element methods on non-matching triangulations.In particular, we discuss and analyze dual Lagrange multiplier spacesfor lowest order finite elements.These non standard Lagrange multiplier spaces yield optimal discretizationschemes and a locally supported basis for the associatedconstrained mortar spaces. As a consequence,standard efficient iterative solvers as multigrid methods or domain decomposition techniques can be easily adapted to the nonconformingsituation.Here, we introduce new dual Lagrange multiplier spaces. We concentrateon the construction of locally supported and continuous dualbasis functions.The optimality of the associated mortar method is shown. Numerical results illustrate the performance of our approach.

Les méthodes sans maillage emploient une interpolation associée à un ensemble de particules : aucune information concernant la connectivité ne doit être fournie.Un des atouts de ces méthodes est que la discrétisationpeut être enrichie d'une façon très simple, soit en augmentant le nombre de particules (analogue à lastratégie de raffinement h), soit en augmentant l'ordre de consistance (analogueà la stratégie de raffinement p). Néanmoins, le coût du calcul des fonctionsd'interpolation est très élevé et ceci représente un inconvénient vis-à-visdes éléments finis. Cet article présente une interpolation mixte élémentsfinis-particules qui résulte de la généralisation de plusieurs travaux dans cedomaine. La formulation de cette interpolation mixte est valable pour n'importe quel ordre de consistance. Dans ce contexte, onénonce un estimateur d'erreur a priori dont la démonstrationse base dans les propriétés de l'interpolation mixte.Ce résultat permet d'étudier la convergence de laméthode d'enrichissement et d'établir les stratégies de raffinement del'interpolation qui permettent d'atteindre une solutionavec une précision satisfaisante.

In this paper, we prove the convergence of the current defined from the Schrödinger-Poisson system with the presence of a strong magnetic field toward a dissipative solution of the Euler equations.

The present paper is devoted to the computation of single phase or two phase flows using the single-fluid approach. Governing equations rely on Euler equations which may be supplemented by conservation laws for mass species. Emphasis is given on numerical modelling with help of Godunov scheme or an approximate form of Godunov scheme called VFRoe-ncv based on velocity and pressure variables. Three distinct classes of closure laws to express the internal energy in terms of pressure, density and additional variables are exhibited. It is shown first that a standard conservative formulation of above mentioned schemes enables to predict “perfectly” unsteady contact discontinuities on coarse meshes, when the equation of state (EOS) belongs to the first class. On the basis of previous work issuing from literature, an almost conservative though modified version of the scheme is proposed to deal with EOS in the second or third class. Numerical evidence shows that the accuracy of approximations of discontinuous solutions of standard Riemann problems is strengthened on coarse meshes, but that convergence towards the right shock solution may be lost in some cases involving complex EOS in the third class. Hence, a blend scheme is eventually proposed to benefit from both properties (“perfect” representation of contact discontinuities on coarse meshes, and correct convergence on finer meshes). Computational results based on an approximate Godunov scheme are provided and discussed.

We analyze the compressible isentropic Navier–Stokes equations (Lions, 1998) in the two-dimensional case with $\gamma=\displaystyle{{c_{p}}/{c_{v}}}=2$ . These equations also modelizethe shallow water problem in height-flow rate formulation used tosolve the flow in lakes and perfectly well-mixed sea. We establisha convergence result for the time-discretized problem when themomentum equation and the continuity equation are solved with theGalerkin method, without adding a penalization term in thecontinuity equation as it is made in Lions (1998). The secondpart is devoted to the numerical analysis and mainly deals withproblems of geophysical fluids. We compare the simulationsobtained with this compressible isentropic Navier–Stokes model andthose obtained with a shallow water model (Di Martino et al., 1999). At first,the computations are executed on a simplified domain in order tovalidate the method by comparison with existing numerical resultsand then on a real domain: the dam of Calacuccia (France). At last, we numerically implement an analyticalexample presented by Weigant (1995) which shows thateven if the data are rather smooth, we cannot have bounds onρ in Lp for p large if $\gamma<2$ when N=2.