35,442 research outputs found
Tensor networks and the numerical renormalization group
The full-density-matrix numerical renormalization group (NRG) has evolved as
a systematic and transparent setting for the cal- culation of thermodynamical
quantities at arbitrary temperatures within the NRG framework. It directly
evaluates the relevant Lehmann representations based on the complete basis sets
intro- duced by Anders and Schiller (2005). In addition, specific attention is
given to the possible feedback from low energy physics to high energies by the
explicit and careful construction of the full thermal density matrix, naturally
generated over a distribution of energy shells. Specific examples are given in
terms of spectral functions (fdmNRG), time-dependent NRG (tdmNRG), Fermi-Golden
rule calculations (fgrNRG), as well as the calculation of plain thermodynamic
expectation values. Furthermore, based on the very fact that, by its iterative
nature, the NRG eigenstates are naturally described in terms of matrix product
states, the language of tensor networks has proven enormously convenient in the
description of the underlying algorithmic procedures. This paper therefore also
provides a detailed introduction and discussion of the prototypical NRG
calculations in terms of their corresponding tensor networks.Comment: 20 pages, 11 figures (adapted from habilitation thesis
Experience with the Open Source based implementation for ATLAS Conditions Data Management System
Conditions Data in high energy physics experiments is frequently seen as
every data needed for reconstruction besides the event data itself. This
includes all sorts of slowly evolving data like detector alignment, calibration
and robustness, and data from detector control system. Also, every Conditions
Data Object is associated with a time interval of validity and a version.
Besides that, quite often is useful to tag collections of Conditions Data
Objects altogether. These issues have already been investigated and a data
model has been proposed and used for different implementations based in
commercial DBMSs, both at CERN and for the BaBar experiment. The special case
of the ATLAS complex trigger that requires online access to calibration and
alignment data poses new challenges that have to be met using a flexible and
customizable solution more in the line of Open Source components. Motivated by
the ATLAS challenges we have developed an alternative implementation, based in
an Open Source RDBMS. Several issues were investigated land will be described
in this paper:
-The best way to map the conditions data model into the relational database
concept considering what are foreseen as the most frequent queries.
-The clustering model best suited to address the scalability problem.
-Extensive tests were performed and will be described.
The very promising results from these tests are attracting the attention from
the HEP community and driving further developments.Comment: 8 pages, 4 figures, 3 tables, conferenc
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