8 research outputs found
On Basis Constructions in Finite Element Exterior Calculus
We give a systematic and self-contained account of the construction of
geometrically decomposed bases and degrees of freedom in finite element
exterior calculus. In particular, we elaborate upon a previously overlooked
basis for one of the families of finite element spaces, which is of interest
for implementations. Moreover, we give details for the construction of
isomorphisms and duality pairings between finite element spaces. These
structural results show, for example, how to transfer linear dependencies
between canonical spanning sets, or give a new derivation of the degrees of
freedom
Symmetry and Invariant Bases in Finite Element Exterior Calculus
We study symmetries of bases and spanning sets in finite element exterior
calculus using representation theory. The group of affine symmetries of a
simplex is isomorphic to a permutation group and represented on simplicial
finite element spaces by the pullback action. We want to know which
vector-valued finite element spaces have bases that are invariant under
permutation of vertex indices. We determine a natural notion of invariance and
sufficient conditions on the dimension and polynomial degree for the existence
of invariant bases. We conjecture that these conditions are necessary too. We
utilize Djokovic and Malzan's classification of monomial irreducible
representations of the symmetric group and use symmetries of the geometric
decomposition and canonical isomorphisms of the finite element spaces.
Invariant bases are constructed in dimensions two and three for different
spaces of finite element differential forms.Comment: 27 pages. Submitte
Conforming Finite Element Function Spaces in Four Dimensions, Part 1: Foundational Principles and the Tesseract
The stability, robustness, accuracy, and efficiency of space-time finite
element methods crucially depend on the choice of approximation spaces for test
and trial functions. This is especially true for high-order, mixed finite
element methods which often must satisfy an inf-sup condition in order to
ensure stability. With this in mind, the primary objective of this paper and a
companion paper is to provide a wide range of explicitly stated, conforming,
finite element spaces in four-dimensions. In this paper, we construct explicit
high-order conforming finite elements on 4-cubes (tesseracts); our construction
uses tools from the recently developed `Finite Element Exterior Calculus'. With
a focus on practical implementation, we provide details including Piola-type
transformations, and explicit expressions for the volumetric, facet, face,
edge, and vertex degrees of freedom. In addition, we establish important
theoretical properties, such as the exactness of the finite element sequences,
and the unisolvence of the degrees of freedom.Comment: 35 pages, 1 figure, 1 tabl