Motif-based Hessian Preconditioner
Computed structure for a 339-atom silicon quantum dot (Si235H104) using a new motif-based Hessian preconditioned CG for the solution of an ab initio atomic relaxation. The unpreconditioned CG method took 31 iterations, where each iteration used on average 140 minutes on 32 processors of the NERSC Seaborg system. The preconditioned CG method took 6 iterations, resulting in a total time savings of 1867 CPU hours per simulation. For details see Motif-based Hessian matrix for ab initio geometry optimization of nanostructures,
Zhao, Wang, and Meza, Technical Report LBNL-59974 (2006).
This project is focused on the
the development of scalable methods for electronic excitation and optical responses of nanostructures. This is a joint BES/OASCR funded project that involves LBNL, UCB, University of Minnesota, University of Texas, and Princeton.
Parallel Optimization
This project is focused on the
the development of optimization algorithms for large-scale scientific and
engineering design problems. Usually these problems involve computationally
expensive objective functions with either no derivative information or
inaccurate gradients. We have been concentrating on both derivative-free
methods and parallel optimization methods that use a combination of direct
search methods and Newton methods.
This is a new area of research that is part of a
recently founded reading group on machine learning at LBNL. In
addition to the group's web pages , I've
also compiled a short overview of ensemble methods for machine
learning at Ensemble
Methods for Machine Learning . To see some Matlab files for
running some simple experiments on reconstructing high-energy
physics tracks using Exemplars go to Track Examples .
Software
Another area of research is the development of object-oriented
software for scientific computing. This work has led to the
development of a package for nonlinear optimization called OPT++ . If
you'd like to learn more about this package, the documentation is
available at OPT++ Documentation
Previous Projects
Optimization in Statistics. These projects involve the use of optimization in statistical problems. One such project
involves the use of optimization for computing MLE's to determine the
best family of distributions for a given data set.
Molecular Conformation. A past interest of mine has been the use of nonlinear optimization methods for solving the molecular conformation
problem. This work led to several papers on the use of direct
search methods as competitors to genetic algorithms and
simulated annealing.