Abstract:
In this paper, it is proved that a Laplace grid operator approximating a Dirichlet boundary value problem for the Poisson equation by the finite element method with piecewise-linear functions on an evenly condensed grid that is topologically equivalent to a rectangular grid (i.e. obtained by shifting the rectangular grid nodes) is equivalent, in the range, to the operator of a $5$-point difference scheme on a uniform grid.
Key words:Dirichlet boundary value problem for the Poisson equation, finite element method with piecewise-linear functions, condensed grid (topologically equivalent to a rectangular grid), preconditioner.