Galerkin projection of discrete fields via supermesh construction

Interpolation of discrete FIelds arises frequently in computational physics. This thesis focuses on the novel implementation and analysis of Galerkin projection, an interpolation technique with three principal advantages over its competitors: it is optimally accurate in the L2 norm, it is conservative, and it is well-defined in the case of spaces of discontinuous functions. While these desirable properties have been known for some time, the implementation of Galerkin projection is challenging; this thesis reports the first successful general implementation. A thorough review of the history, development and current frontiers of adaptive remeshing is given. Adaptive remeshing is the primary motivation for the development of Galerkin projection, as its use necessitates the interpolation of discrete fields. The Galerkin projection is discussed and the geometric concept necessary for its implementation, the supermesh, is introduced. The efficient local construction of the supermesh of two meshes by the intersection of the elements of the input meshes is then described. Next, the element-element association problem of identifying which elements from the input meshes intersect is analysed. With efficient algorithms for its construction in hand, applications of supermeshing other than Galerkin projections are discussed, focusing on the computation of diagnostics of simulations which employ adaptive remeshing. Examples demonstrating the effectiveness and efficiency of the presented algorithms are given throughout. The thesis closes with some conclusions and possibilities for future work

Reporting intersecting pairs of polytopes in two and three dimensions

Let P={P 1,...,P m} be a set of m convex polytopes in Rd, for d = 2,3, with a total of n vertices. We present output-sensitive algorithms for reporting all k pairs of indices (i, j) such that P i intersects P j. For the planar case we describe a simple algorithm with running time O(n 4/3logn + k), and an improved randomized algorithm with expected running time O((n log m + k)a(n)logn) (which is faster for small values of k). For d = 3, we present an O(n 8/5+e + k)-time algorithm, for any e>0. Our algorithms can be modified to count the number of intersecting pairs in O(n 4/3 log O(1) n) time for the planar case, and in O(n 8/5+e) time and R3. P.A. was also supported by Army Research Office MURI grant DAAH04-96-1-0013, by a Sloan fellowship, by NSF grants EIA-9870724, EIA-997287, and CCR-9732787, and by a grant from the U.S.-Israeli Binational Science Foundation. M.S. was supported by NSF Grant CCR-97-32101, by a grant from the Israel Science Fund (for a Center of Excellence in Geometric Computing), by the Hermann Minkowski-MINERVA Center for Geometry at Tel Aviv University, and by a grant from the U.S.-Israeli Binational Science Foundation

Reporting Intersecting Pairs of Polytopes in Two and Three Dimensions

Let P={P 1,...,P m} be a set of m convex polytopes in Rd, for d = 2,3, with a total of n vertices. We present output-sensitive algorithms for reporting all k pairs of indices (i, j) such that P i intersects P j. For the planar case we describe a simple algorithm with running time O(n 4/3logn + k), and an improved randomized algorithm with expected running time O((n log m + k)a(n)logn) (which is faster for small values of k). For d = 3, we present an O(n 8/5+e + k)-time algorithm, for any e>0. Our algorithms can be modified to count the number of intersecting pairs in O(n 4/3 log O(1) n) time for the planar case, and in O(n 8/5+e) time and R3. P.A. was also supported by Army Research Office MURI grant DAAH04-96-1-0013, by a Sloan fellowship, by NSF grants EIA-9870724, EIA-997287, and CCR-9732787, and by a grant from the U.S.-Israeli Binational Science Foundation. M.S. was supported by NSF Grant CCR-97-32101, by a grant from the Israel Science Fund (for a Center of Excellence in Geometric Computing), by the Hermann Minkowski-MINERVA Center for Geometry at Tel Aviv University, and by a grant from the U.S.-Israeli Binational Science Foundation

Reporting Intersecting Pairs of Polytopes in Two and Three Dimensions

Let P = fP1 ; : : : ; Pmg be a set of m convex polytopes in R d , for d = 2; 3, with a total of n vertices. We present output-sensitive algorithms for reporting all k pairs of indices (i; j) such that P i intersects P j . For the planar case we describe a simple algorithm with running time O(n 4=3 log n+k), and an improved randomized algorithm with expected running time O((n log m+k)ff(n) log n) (which is faster for small values of k). For d = 3, we present an O(n 8=5+" +k)-time algorithm, for any " ? 0