Publications

Results 51–75 of 235
Skip to search filters

The pitfalls of provisioning exascale networks: A trace replay analysis for understanding communication performance

Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)

Kenny, Joseph P.; Sargsyan, Khachik S.; Knight, Samuel K.; Michelogiannakis, George; Wilke, Jeremiah J.

Data movement is considered the main performance concern for exascale, including both on-node memory and off-node network communication. Indeed, many application traces show significant time spent in MPI calls, potentially indicating that faster networks must be provisioned for scalability. However, equating MPI times with network communication delays ignores synchronization delays and software overheads independent of network hardware. Using point-to-point protocol details, we explore the decomposition of MPI time into communication, synchronization and software stack components using architecture simulation. Detailed validation using Bayesian inference is used to identify the sensitivity of performance to specific latency/bandwidth parameters for different network protocols and to quantify associated uncertainties. The inference combined with trace replay shows that synchronization and MPI software stack overhead are at least as important as the network itself in determining time spent in communication routines.

More Details
TYPE Conference Poster YEAR 2018
ScopusOSTI

UQTk Version 3.0.4 User Manual

Sargsyan, Khachik S.; Safta, Cosmin S.; Chowdhary, Kamaljit S.; Castorena, Sarah C.; de Bord, Sarah d.; Debusschere, Bert D.

The UQ Toolkit (UQTk) is a collection of libraries and tools for the quantification of uncertainty in numerical model predictions. Version 3.0.4 offers intrusive and non-intrusive methods for propagating input uncertainties through computational models, tools for sensitivity analysis, methods for sparse surrogate construction, and Bayesian inference tools for inferring parameters from experimental data. This manual discusses the download and installation process for UQTk, provides pointers to the UQ methods used in the toolkit, and describes some of the examples provided with the toolkit.

More Details
TYPE SAND Report YEAR 2017
OSTIDOI

Low-rank canonical-tensor decomposition of potential energy surfaces: application to grid-based diagrammatic vibrational Green’s function theory

Molecular Physics

Rai, Prashant R.; Sargsyan, Khachik S.; Najm, H.N.; Hermes, Matthew R.; Hirata, So

A new method is proposed for a fast evaluation of high-dimensional integrals of potential energy surfaces (PES) that arise in many areas of quantum dynamics. It decomposes a PES into a canonical low-rank tensor format, reducing its integral into a relatively short sum of products of low-dimensional integrals. The decomposition is achieved by the alternating least squares (ALS) algorithm, requiring only a small number of single-point energy evaluations. Therefore, it eradicates a force-constant evaluation as the hotspot of many quantum dynamics simulations and also possibly lifts the curse of dimensionality. This general method is applied to the anharmonic vibrational zero-point and transition energy calculations of molecules using the second-order diagrammatic vibrational many-body Green's function (XVH2) theory with a harmonic-approximation reference. In this application, high dimensional PES and Green's functions are both subjected to a low-rank decomposition. Evaluating the molecular integrals over a low-rank PES and Green's functions as sums of low-dimensional integrals using the Gauss–Hermite quadrature, this canonical-tensor-decomposition-based XVH2 (CT-XVH2) achieves an accuracy of 0.1 cm−1 or higher and nearly an order of magnitude speedup as compared with the original algorithm using force constants for water and formaldehyde.

More Details
TYPE Journal Article YEAR 2017
ScopusOSTIDOI

Uncertainty quantification toolkit (UQTk)

Handbook of Uncertainty Quantification

Debusschere, Bert D.; Sargsyan, Khachik S.; Safta, Cosmin S.; Chowdhary, Kenny

The UQ Toolkit (UQTk) is a collection of tools for uncertainty quantification, ranging from intrusive and nonintrusive forward propagation of uncertainty to inverse problems and sensitivity analysis. This chapter first outlines the UQTk design philosophy, followed by an overview of the available methods and the way they are implemented in UQTk. The second part of this chapter is a detailed example that illustrates a UQ workflow from surrogate construction, and calibration, to forward propagation and attribution.

More Details
TYPE Book YEAR 2017
ScopusOSTI

UQTk Version 3.0.3 User Manual

Sargsyan, Khachik S.; Safta, Cosmin S.; Chowdhary, Kamaljit S.; Castorena, Sarah C.; de Bord, Sarah d.; Debusschere, Bert D.

The UQ Toolkit (UQTk) is a collection of libraries and tools for the quantification of uncertainty in numerical model predictions. Version 3.0.3 offers intrusive and non-intrusive methods for propagating input uncertainties through computational models, tools for sen- sitivity analysis, methods for sparse surrogate construction, and Bayesian inference tools for inferring parameters from experimental data. This manual discusses the download and installation process for UQTk, provides pointers to the UQ methods used in the toolkit, and describes some of the examples provided with the toolkit.

More Details
TYPE SAND Report YEAR 2017
OSTIDOI
Results 51–75 of 235
Results 51–75 of 235