959 research outputs found
Block Locally Optimal Preconditioned Eigenvalue Xolvers (BLOPEX) in hypre and PETSc
We describe our software package Block Locally Optimal Preconditioned
Eigenvalue Xolvers (BLOPEX) publicly released recently. BLOPEX is available as
a stand-alone serial library, as an external package to PETSc (``Portable,
Extensible Toolkit for Scientific Computation'', a general purpose suite of
tools for the scalable solution of partial differential equations and related
problems developed by Argonne National Laboratory), and is also built into {\it
hypre} (``High Performance Preconditioners'', scalable linear solvers package
developed by Lawrence Livermore National Laboratory). The present BLOPEX
release includes only one solver--the Locally Optimal Block Preconditioned
Conjugate Gradient (LOBPCG) method for symmetric eigenvalue problems. {\it
hypre} provides users with advanced high-quality parallel preconditioners for
linear systems, in particular, with domain decomposition and multigrid
preconditioners. With BLOPEX, the same preconditioners can now be efficiently
used for symmetric eigenvalue problems. PETSc facilitates the integration of
independently developed application modules with strict attention to component
interoperability, and makes BLOPEX extremely easy to compile and use with
preconditioners that are available via PETSc. We present the LOBPCG algorithm
in BLOPEX for {\it hypre} and PETSc. We demonstrate numerically the scalability
of BLOPEX by testing it on a number of distributed and shared memory parallel
systems, including a Beowulf system, SUN Fire 880, an AMD dual-core Opteron
workstation, and IBM BlueGene/L supercomputer, using PETSc domain decomposition
and {\it hypre} multigrid preconditioning. We test BLOPEX on a model problem,
the standard 7-point finite-difference approximation of the 3-D Laplacian, with
the problem size in the range .Comment: Submitted to SIAM Journal on Scientific Computin
Bounds on changes in Ritz values for a perturbed invariant subspace of a Hermitian matrix
The Rayleigh-Ritz method is widely used for eigenvalue approximation. Given a
matrix with columns that form an orthonormal basis for a subspace \X, and
a Hermitian matrix , the eigenvalues of are called Ritz values of
with respect to \X. If the subspace \X is -invariant then the Ritz
values are some of the eigenvalues of . If the -invariant subspace \X
is perturbed to give rise to another subspace \Y, then the vector of absolute
values of changes in Ritz values of represents the absolute eigenvalue
approximation error using \Y. We bound the error in terms of principal angles
between \X and \Y. We capitalize on ideas from a recent paper [DOI:
10.1137/060649070] by A. Knyazev and M. Argentati, where the vector of absolute
values of differences between Ritz values for subspaces \X and \Y was
weakly (sub-)majorized by a constant times the sine of the vector of principal
angles between \X and \Y, the constant being the spread of the spectrum of
. In that result no assumption was made on either subspace being
-invariant. It was conjectured there that if one of the trial subspaces is
-invariant then an analogous weak majorization bound should only involve
terms of the order of sine squared. Here we confirm this conjecture.
Specifically we prove that the absolute eigenvalue error is weakly majorized by
a constant times the sine squared of the vector of principal angles between the
subspaces \X and \Y, where the constant is proportional to the spread of
the spectrum of . For many practical cases we show that the proportionality
factor is simply one, and that this bound is sharp. For the general case we can
only prove the result with a slightly larger constant, which we believe is
artificial.Comment: 12 pages. Accepted to SIAM Journal on Matrix Analysis and
Applications (SIMAX
Theoretical investigation of TbNi_{5-x}Cu_x optical properties
In this paper we present theoretical investigation of optical conductivity
for intermetallic TbNi_{5-x}Cu_x series. In the frame of LSDA+U calculations
electronic structure for x=0,1,2 and on top of that optical conductivities were
calculated. Disorder effects of Ni for Cu substitution on a level of LSDA+U
densities of states (DOS) were taken into account via averaging over all
possible Cu ion positions for given doping level x. Gradual suppression and
loosing of structure of optical conductivity at 2 eV together with simultaneous
intensity growth at 4 eV correspond to increase of Cu and decrease of Ni
content. As reported before [Knyazev et al., Optics and Spectroscopy 104, 360
(2008)] plasma frequency has non monotonic doping behaviour with maximum at
x=1. This behaviour is explained as competition between lowering of total
density of states on the Fermi level N(E_F) and growing of number of carriers.
Our theoretical results agree well with variety of recent experiments.Comment: 4 pages, 3 figure
Method of variational calculation of influence of the propulsion plants of forestry machines upon the frozen and thawing soil grounds
The forests, which grow in the conditions of complete expansion of the perpetually frozen ground, are unique forests in accordance with their taxational characteristics, quality indicators of the felled timber, and the ecological functions, which these forests perform in the nature. They are characterised by the low biological productivity, as well as by the high vulnerability due to climatological changes and human economic activities. It is fair to say that conservation of the permafrost is one of the main functions of the forests, which grow within the cryolithozone. Because of this, it is necessary to ensure special regimes for the forestry management and forest exploitation within the forests of the cryolithozone. We formulated the variational problem in order to determine influence of the changeability of the physical and mechanical properties of the thawing soil ground at the boundary with the permafrost ground. Β© 2019 SERSC
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Currently the issues of alternative use of chemical wastes, which have significan
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