Engineering topics

Ormand, W. Erich

Publications and source records attributed to Ormand, W. Erich.

3 records

DOE OSTI2018

2018 Annual Continuation And Progress Report For Nuclear Theory At Lawrence Livermore National Laboratory

Research in the area of nuclear structure and reactions, with an emphasis on ab initio approaches, was been conducted under base research funding (FWP SCW0498) and the Topical Collaboration (TC) “DBD: Nuclear Theory for Double-Beta Decay and Fundamental Symmetries” (FWP SCW1579). New funding under FWP SCW0498 in FY19 was $130k and, which augmented carryover from the previous year, which was primarily intended to fund an FRIB Theory Fellow. In the period covered by this review, we generated 9 publications (including a Letter, two submissions to Nature, and an invited review paper), and 3 invited talks. In the following we highlight the most important accomplishments.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2015

Parallel implementation and performance optimization of the configuration-interaction method

The configuration-interaction (CI) method, long a popular approach to describe quantum many-body systems, is cast as a very large sparse matrix eigenpair problem with matrices whose dimension can exceed one billion. Such formulations place high demands on memory capacity and memory bandwidth - - two quantities at a premium today. In this paper, we describe an efficient, scalable implementation, BIGSTICK, which, by factorizing both the basis and the interaction into two levels, can reconstruct the nonzero matrix elements on the fly, reduce the memory requirements by one or two orders of magnitude, and enable researchers to trade reduced resources for increased computational time. We optimize BIGSTICK on two leading HPC platforms - - the Cray XC30 and the IBM Blue Gene/Q. Specifically, we not only develop an empirically-driven load balancing strategy that can evenly distribute the matrix-vector multiplication across 256K threads, we also developed techniques that improve the performance of the Lanczos reorthogonalization. Combined, these optimizations improved performance by 1.3-8× depending on platform and configuration.

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2013

Factorization in large-scale many-body calculations

One approach for solving interacting many-fermion systems is the configuration-interaction method, also sometimes called the interacting shell model, where one finds eigenvalues of the Hamiltonian in a many-body basis of Slater determinants (antisymmetrized products of single-particle wavefunctions). The resulting Hamiltonian matrix is typically very sparse, but for large systems the nonzero matrix elements can nonetheless require terabytes or more of storage. An alternate algorithm, applicable to a broad class of systems with symmetry, in our case rotational invariance, is to exactly factorize both the basis and the interaction using additive/multiplicative quantum numbers; such an algorithm recreates the many-body matrix elements on the fly and can reduce the storage requirements by an order of magnitude or more. Here, we discuss factorization in general and introduce a novel, generalized factorization method, essentially a ‘double-factorization’ which speeds up basis generation and set-up of required arrays. Although we emphasize techniques, we also place factorization in the context of a specific (unpublished) configuration-interaction code, BIGSTICK, which runs both on serial and parallel machines, and discuss the savings in memory due to factorization.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗