Collaborative Research: Elements: A task-based code for multiphysics problems in astrophysics at exascale

当前和未来的计算机将以百亿亿次运行，比今天的典型机器强大100多倍。当前代码中使用的许多算法将无法利用这些新机器。研究人员将完成天体物理学和引力物理学中多尺度、多物理场问题的开源社区代码的开发。代码使用转换算法达到百亿亿次。这些技术可以应用于流体动力学、地球科学、等离子体物理和核物理与工程等学科。这种新代码的开发是由目前部署的引力波探测器（如LIGO）推动的。为了充分理解和分析用这种探测器测量的信号和波形，必须有准确、健壮和高效的计算工具来解决很长时间尺度上的动态爱因斯坦方程。最近由LIGO和许多电磁望远镜探测到的中子星合并，开启了多信使天文学的时代。物质和辐射的极端能量密度以及这些事件的高度动态时空探索了地面实验无法达到的基本物理。新代码将作为开源社区网络基础设施提供。研究人员将接触天体物理学的其他领域（如恒星形成、空间等离子体物理学），并跨越流体动力学、地球科学、等离子体物理学、核工程等学科界限。无论是在学术界还是作为高技能的工业STEM劳动力，对受过这些技术培训的年轻研究人员的需求都很大。本科生将通过制作可视化来参与研究。新代码使用不连续的Galerkin方法和基于任务的并行性来实现预期的目标。该框架将允许在千兆级和百亿亿级机器的新架构上准确有效地处理多物理场应用程序。该代码旨在扩展到超过一百万个核心，以有效地探索潜在源和允许物理的参数空间，以及实现多信使天文学承诺所需的高保真度预测。该代码将允许天体物理学家探索驱动核心坍缩超新星的机制和恒星残骸的特性，理解致密物体中的电磁瞬变和引力波现象，并揭示致密物质的状态方程。代码中的两个关键算法创新，不连续伽辽金方法与基于任务的并行性相结合，有望在其他领域产生革命性的影响，这些领域依赖于百亿亿级偏微分方程的数值解。该项目推进了“宇宙之窗：多信使天体物理学时代”的目标，这是美国国家科学基金会未来投资的十大理念之一。该项目还推进了国家战略计算计划（NSCI）的目标，该计划旨在维持和加强美国在高性能计算（HPC）研究、开发和部署方面的科学、技术和经济领导地位。该项目由计算机与信息科学与工程理事会的高级网络基础设施办公室以及数学与物理科学理事会的物理系和天文科学系提供支持。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Current and upcoming computers will run at exascale, over a hundred times more powerful than typical machines of today. Many algorithms used in current codes will not be able to take advantage of these new machines. The researchers will complete the development of an open-source community code for multi-scale, multi-physics problems in astrophysics and gravitational physics. The code uses transformative algorithms to reach the exascale. The techniques can be applied across discipline boundaries in fluid dynamics, geoscience, plasma physics and nuclear physics and engineering. The development of this new code has been driven by the current deployment of gravitational wave detectors such as LIGO. To fully understand and analyze the signals and waveforms measured with such detectors, it is essential that accurate, robust, and efficient computational tools be available for solving the dynamical Einstein equations over very long time scales. The recent detection of the merger of a neutron star-neutron star merger by LIGO and by a host of electromagnetic telescopes has ushered in the era of multi-messenger astronomy. The extreme energy densities of matter and radiation and the highly dynamic spacetimes of these events probe fundamental physics inaccessible to terrestrial experiments. The new code will be made available as open-source community cyberinfrastructure. The researchers will reach out to other communities within astrophysics (e.g., star formation, space plasma physics) and across discipline boundaries to fluid dynamics, geoscience, plasma physics, nuclear engineering etc. Young researchers trained in these techniques are in great demand, both in academia and as highly-skilled members of the industrial STEM workforce. Undergraduates will participate in the research by producing visualizations.The new code uses discontinuous Galerkin methods and task-based parallelism to accomplish its desired goals. This framework will allow the multi-physics applications to be treated both accurately and efficiently on the new architectures of petascale and exascale machines. The code is designed to scale to over a million cores for efficient exploration of the parameter space of potential sources and allowed physics, and for the high-fidelity predictions needed to realize the promise of multi-messenger astronomy. The code will allow astrophysicists to explore the mechanisms driving core-collapse supernovae and the properties of stellar remnants, to understand electromagnetic transients and gravitational-wave phenomena in compact objects, and to reveal the dense matter equation of state. The two key algorithmic innovations in the code, the discontinuous Galerkin method coupled with task-based parallelism, promise revolutionary impact in other fields relying on numerical solution of partial differential equations at the exascale.This project advances the objectives of "Windows on the Universe: the Era of Multi-Messenger Astrophysics", one of the 10 Big Ideas for Future NSF Investments. This project advances also the objectives of the National Strategic Computing Initiative (NSCI), an effort aimed at sustaining and enhancing the U.S. scientific, technological, and economic leadership position in High-Performance Computing (HPC) research, development, and deployment.This project is supported by the Office of Advanced Cyberinfrastructure in the Directorate for Computer & Information Science & Engineering and the Division of Physics and the Division of Astronomical Sciences in the Directorate of Mathematical and Physical Sciences.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.