## On diagonal dominance of stiffness matrices in 3D.(English)Zbl 0824.65112

A class of nonlinear elliptic boundary value problems on polyhedral domains which are approximated by standard linear tetrahedral elements are considered. The problems under consideration describe magnetic fields, nonviscous subsonic irrotational flows, nonlinear heat conduction in isotropic media, etc. As the continuous problem satisfies the maximum principle, the authors introduce an acute type condition upon the partitions of the domain which guarantees that the discrete problem satisfies the discrete maximum principle. It is proven that the corresponding stiffness matrix is irreducibly diagonally dominant if all internal angles between the faces of the tetrahedra are not greater than $$\pi/2$$. Using this fact, the satisfaction of the discrete maximum principle is shown.
Some examples of acute type decompositions (all six internal angles between the faces of any tetrahedron are not greater than $$\pi/2$$) are presented.
Reviewer: K.Georgiev (Sofia)

### MSC:

 65N30 Finite element, Rayleigh-Ritz and Galerkin methods for boundary value problems involving PDEs 65N55 Multigrid methods; domain decomposition for boundary value problems involving PDEs 65F10 Iterative numerical methods for linear systems 35J65 Nonlinear boundary value problems for linear elliptic equations