Software for Exascale Computing - SPPEXA 2016-2019

This open access book summarizes the research done and results obtained in the second funding phase of the Priority Program 1648 "Software for Exascale Computing" (SPPEXA) of the German Research Foundation (DFG) presented at the SPPEXA Symposium in Dresden during October 21-23, 2019. In that respect, it both represents a continuation of Vol. 113 in Springer’s series Lecture Notes in Computational Science and Engineering, the corresponding report of SPPEXA’s first funding phase, and provides an overview of SPPEXA’s contributions towards exascale computing in today's sumpercomputer technology. The individual chapters address one or more of the research directions (1) computational algorithms, (2) system software, (3) application software, (4) data management and exploration, (5) programming, and (6) software tools. The book has an interdisciplinary appeal: scholars from computational sub-fields in computer science, mathematics, physics, or engineering will find it of particular interest

Floorplan-guided placement for large-scale mixed-size designs

In the nanometer scale era, placement has become an extremely challenging stage in modern Very-Large-Scale Integration (VLSI) designs. Millions of objects need to be placed legally within a chip region, while both the interconnection and object distribution have to be optimized simultaneously. Due to the extensive use of Intellectual Property (IP) and embedded memory blocks, a design usually contains tens or even hundreds of big macros. A design with big movable macros and numerous standard cells is known as mixed-size design. Due to the big size difference between big macros and standard cells, the placement of mixed-size designs is much more difficult than the standard-cell placement. This work presents an efficient and high-quality placement tool to handle modern large-scale mixed-size designs. This tool is developed based on a new placement algorithm flow. The main idea is to use the fixed-outline floorplanning algorithm to guide the state-of-the-art analytical placer. This new flow consists of four steps: 1) The objects in the original netlist are clustered into blocks; 2) Floorplanning is performed on the blocks; 3) The blocks are shifted within the chip region to further optimize the wirelength; 4) With big macro locations fixed, incremental placement is applied to place the remaining objects. Several key techniques are proposed to be used in the first two steps. These techniques are mainly focused on the following two aspects: 1) Hypergraph clustering algorithm that can cut down the original problem size without loss of placement Quality of Results (QoR); 2) Fixed-outline floorplanning algorithm that can provide a good guidance to the analytical placer at the global level. The effectiveness of each key technique is demonstrated by promising experimental results compared with the state-of-the-art algorithms. Moreover, using the industrial mixed-size designs, the new placement tool shows better performance than other existing approaches

Multigrid barrier and penalty methods for large scale topology optimization of solid structures

We propose two algorithms for solving minimum compliance topology optimization problems defined on finite element meshes with several million elements, where the design geometry is parameterized on the discretized problem domain by an elementwise constant density field and we use the variable thickness sheet formulation to map the density to the material stiffness. The first method is an interior point (IP) method and the second follows the penalty-barrier multiplier (PBM) or nonlinear rescaling framework. To solve the linear systems arising in each optimization iteration, we use a multigrid-preconditioned Krylov solver. We employ a reformulation of the linear system to obtain a symmetric positive definite matrix that is amenable to standard multigrid transfer operators. We test the performance of both our algorithms on a wide range of numerical examples, comparing their performance to each other and to that of the well-established optimality criteria (OC) method. Our PBM algorithm proves to be more robust and efficient than both the IP and OC method. We then extend our approach to problems defined on unstructured meshes, which necessitates switching to an algebraic multigrid preconditioner. Using the (adaptive) smoothed aggregation method of Vaněk, Mandel, and Brezina, we propose and test different non-standard setup strategies for the multigrid transfer operators in order to identify the most efficient one for our type of problem. The PBM method is applied to the dual of the compliance minimization problem, which permits an easy integration of unilateral contact constraints. We include examples featuring such constraints in our numerical experiments, both for problems on uniform structured meshes and on unstructured meshes

Research in progress and other activities of the Institute for Computer Applications in Science and Engineering

This report summarizes research conducted at the Institute for Computer Applications in Science and Engineering in applied mathematics and computer science during the period April 1, 1993 through September 30, 1993. The major categories of the current ICASE research program are: (1) applied and numerical mathematics, including numerical analysis and algorithm development; (2) theoretical and computational research in fluid mechanics in selected areas of interest to LaRC, including acoustic and combustion; (3) experimental research in transition and turbulence and aerodynamics involving LaRC facilities and scientists; and (4) computer science