1,372 research outputs found
High precision simulations of weak lensing effect on Cosmic Microwave Background polarization
We study accuracy, robustness and self-consistency of pixel-domain
simulations of the gravitational lensing effect on the primordial CMB
anisotropies due to the large-scale structure of the Universe. In particular,
we investigate dependence of the results precision on some crucial parameters
of such techniques and propose a semi-analytic framework to determine their
values so the required precision is a priori assured and the numerical workload
simultaneously optimized. Our focus is on the B-mode signal but we discuss also
other CMB observables, such as total intensity, T, and E-mode polarization,
emphasizing differences and similarities between all these cases. Our
semi-analytic considerations are backed up by extensive numerical results.
Those are obtained using a code, nicknamed lenS2HAT -- for Lensing using
Scalable Spherical Harmonic Transforms (S2HAT) -- which we have developed in
the course of this work. The code implements a version of the pixel-domain
approach of Lewis (2005) and permits performing the simulations at very high
resolutions and data volumes, thanks to its efficient parallelization provided
by the S2HAT library -- a parallel library for a calculation of the spherical
harmonic transforms. The code is made publicly available.Comment: 20 pages, 14 figures, submitted to A&A, matches version accepted for
publication in A&
Autonomous Volterra algorithm for steady-state analysis of nonlinear circuits
published_or_final_versio
Linear scaling computation of the Fock matrix. IX. Parallel computation of the Coulomb matrix
We present parallelization of a quantum-chemical tree-code [J. Chem. Phys.
{\bf 106}, 5526 (1997)] for linear scaling computation of the Coulomb matrix.
Equal time partition [J. Chem. Phys. {\bf 118}, 9128 (2003)] is used to load
balance computation of the Coulomb matrix. Equal time partition is a
measurement based algorithm for domain decomposition that exploits small
variation of the density between self-consistent-field cycles to achieve load
balance. Efficiency of the equal time partition is illustrated by several tests
involving both finite and periodic systems. It is found that equal time
partition is able to deliver 91 -- 98 % efficiency with 128 processors in the
most time consuming part of the Coulomb matrix calculation. The current
parallel quantum chemical tree code is able to deliver 63 -- 81% overall
efficiency on 128 processors with fine grained parallelism (less than two heavy
atoms per processor).Comment: 7 pages, 6 figure
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