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The convergence of extremely high levels of hardware concurrency and the effective overlap of computation and communication in asynchronous executions has resulted in increasing nondeterminism in High-Performance Computing (HPC) applications. Nondeterminism can manifest at multiple levels: from low-level communication primitives to libraries to application-level functions. No matter its source, nondeterminism can drastically increase the cost of result reproducibility, debugging workflows, testing parallel programs, or ensuring fault-tolerance. Nondeterministic executions of HPC applications can be modeled as event graphs, and the applications’ nondeterministic behavior can be understood and, in some cases, mitigated using graph comparison algorithms. However, a connection between graph comparison algorithms and approaches to understanding nondeterminism in HPC still needs to be established. This survey article moves the first steps toward establishing a connection between graph comparison algorithms and nondeterminism in HPC with its three contributions: it provides a survey of different graph comparison algorithms and a timeline for each category’s significant works; it discusses how existing graph comparison methods do not fully support properties needed to understand nondeterministic patterns in HPC applications; and it presents the open challenges that should be addressed to leverage the power of graph comparisons for the study of nondeterminism in HPC applications. 

Confocal microscopes are known for optically removing the out-of-focus information (i.e., blur) in each transverse section of the sample’s volume, providing a more accurate three-dimensional image of thick microscopic samples than widefield microscopes. In this work, we have designed and evaluated a confocal microscope using off-of-shelf optical components from Thorlabs’ catalog, one of the major optical manufacturers. The design and evaluation have been implemented using Zemax OpticStudio, the standard optical system design software for realistic optical simulation. Here, we have also reported a practical protocol for building a confocal microscope using sequential mode.