378	RWTH Publication No: 230395        2013        IGPM378.pdf
TITLE	Legendre-Gauss-Lobatto Grids and Associated Nested Dyadic Grids
AUTHORS	Kolja Brix, Claudio Canuto, Wolfgang Dahmen
ABSTRACT	Legendre-Gauss-Lobatto (LGL) grids play a pivotal role in nodal spectral methods for the numerical solution of partial differential equations. They not only provide efficient high-order quadrature rules, but give also rise to norm equivalences that could eventually lead to efficient preconditioning techniques in high-order methods. Unfortunately, a serious obstruction to fully exploiting the potential of such concepts is the fact that LGL grids of different degree are not nested. This affects, on the one hand, the choice and analysis of suitable auxiliary spaces, when applying the auxiliary space method as a principal preconditioning paradigm, and, on the other hand, the efficient solution of the auxiliary problems. As a central remedy, we consider certain nested hierarchies of dyadic grids of locally comparable mesh size, that are in a certain sense properly associated with the LGL grids. Their actual suitability requires a subtle analysis of such grids which, in turn, relies on a number of refined properties of LGL grids. The central objective of this paper is to derive just these properties. This requires first revisiting properties of close relatives to LGL grids which are subsequently used to develop a refined analysis of LGL grids. These results allow us then to derive the relevant properties of the associated dyadic grids.
KEYWORDS	Legendre-Gauss-Lobatto grid, dyadic grid, graded grid, nested grids
DOI	10.1007/s00211-014-0691-4
PUBLICATION	Nested dyadic grids associated with Legendre–Gauss–Lobatto grids. Numerische Mathematik, 2014 Volume 131, Issue 2, 20015, pp. 205-239
CORRESPONDING AUTHOR	Wolfgang Dahmen