Rough Gauge Fields, Smearing and Domain Wall Fermions

At a fixed lattice spacing, as determined by say m_\rho, adding additional fermion flavors to a dynamical simulation produces rougher gauge field configurations at the lattice scale. For domain wall fermions, these rough configurations lead to larger residual chiral symmetry breaking and larger values for the residual masses, m_{res}. We discuss ongoing attempts to reduce chiral symmetry breaking for N_f = 3 dynamical domain wall fermion simulations by different smoothing choices for the gauge fields.Comment: 3 pages, 2 figures. Talk presented at Lattice2004(chiral), Fermilab, June 21-26, 200

Performance Portability Strategies for Grid C++ Expression Templates

One of the key requirements for the Lattice QCD Application Development as part of the US Exascale Computing Project is performance portability across multiple architectures. Using the Grid C++ expression template as a starting point, we report on the progress made with regards to the Grid GPU offloading strategies. We present both the successes and issues encountered in using CUDA, OpenACC and Just-In-Time compilation. Experimentation and performance on GPUs with a SU(3)$\times$SU(3) streaming test will be reported. We will also report on the challenges of using current OpenMP 4.x for GPU offloading in the same code.Comment: 8 pages, 4 figures. Talk presented at the 35th International Symposium on Lattice Field Theory, 18-24 June 2017, Granada, Spai

Nucleon structure from 2+1-flavor dynamical DWF lattice QCD at nearly physical pion mass

Domain-wall fermions (DWF) is a lattice discretization for Dirac fields that preserves continuum-like chiral and flavor symmetries that are essential in hadron physics. RIKEN-BNL-Columbia (RBC) and UKQCD Collaborations have been generating sets of realistic 2+1-flavor dynamical lattice quantum chromodynamics (QCD) numerical ensembles with DWF quarks with strange mass set almost exactly at its physical value via reweighing and degenerate up and down mass set as light as practical. In this report the current status of the nucleon-structure calculations using these ensembles are summarized.Comment: 7 pages, 5 figures, talk presented at Erice School "From Quarks and Gluons to Hadrons and Nuclei,'' September 16-24, 2011, Erice, Sicil