74,496 research outputs found
Efficacy of the SU(3) scheme for ab initio large-scale calculations beyond the lightest nuclei
We report on the computational characteristics of ab initio nuclear structure
calculations in a symmetry-adapted no-core shell model (SA-NCSM) framework. We
examine the computational complexity of the current implementation of the
SA-NCSM approach, dubbed LSU3shell, by analyzing ab initio results for 6Li and
12C in large harmonic oscillator model spaces and SU(3)-selected subspaces. We
demonstrate LSU3shell's strong-scaling properties achieved with highly-parallel
methods for computing the many-body matrix elements. Results compare favorably
with complete model space calculations and significant memory savings are
achieved in physically important applications. In particular, a well-chosen
symmetry-adapted basis affords memory savings in calculations of states with a
fixed total angular momentum in large model spaces while exactly preserving
translational invariance.Comment: 11 pages, 8 figure
Capturing translational divergences with a statistical tree-to-tree aligner
Parallel treebanks, which comprise paired source-target parse trees aligned at sub-sentential level, could be useful
for many applications, particularly data-driven machine translation. In this paper, we focus on how translational
divergences are captured within a parallel treebank using a fully automatic statistical tree-to-tree aligner. We
observe that while the algorithm performs well at the phrase level, performance on lexical-level alignments
is compromised by an inappropriate bias towards coverage rather than precision. This preference for high precision
rather than broad coverage in terms of expressing translational divergences through tree-alignment stands in
direct opposition to the situation for SMT word-alignment models. We suggest that this has implications not only
for tree-alignment itself but also for the broader area of induction of syntaxaware models for SMT
- …