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

即将到来的计算机将以艾级运行，比今天的典型计算机强大一百多倍。当前代码中使用的许多算法将无法利用这些新机器。研究人员将完成针对天体物理和引力物理中多尺度、多物理问题的开源社区代码的开发。该代码使用变革性算法来达到艾级。这些技术可以应用于流体力学、地球科学、等离子体物理、核物理和工程等学科的跨学科边界。这一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求解很长时间尺度上的动态爱因斯坦方程。最近LIGO和一系列电磁望远镜探测到了中子星-中子星的合并，带来了物质和辐射的极端能量密度，以及这些事件探测基础物理的高动态时空，地球实验无法获得这些事件。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(例如恒星形成、空间等离子体物理)以及跨学科边界到流体动力学、地球科学、等离子体物理、核工程等领域的其他社区。受过这些技术培训的早期职业研究人员在学术界和工业STEM劳动力中都非常需要。本科生将通过生成可视化来参与研究。新代码使用不连续的Galerkin方法和基于任务的并行来实现预期的目标。该框架将允许在新的千兆级和百亿级机器体系结构上准确和高效地处理多物理应用程序。该代码旨在扩展到100多万个核心，以有效地探索潜在源和允许的物理学的参数空间，并实现实现多信使天体物理前景所需的高保真预测。该代码将允许天体物理学家探索驱动核心塌缩超新星的机制和恒星残留物的性质，了解致密天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Galerkin方法与基于任务的并行，有望在其他领域产生革命性的影响，依赖于偏微分方程组的数值解。该项目推进了未来NSF投资的十大想法之一的“宇宙之窗：多信使天体物理时代”的目标。该项目还推进了国家战略计算倡议(NSCI)的目标，该倡议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、技术和经济领先地位。这个项目得到了计算机与信息科学与工程局的高级网络基础设施办公室和数学与物理科学局的物理部和天文科学部的支持。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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 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. Early-career 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 multiphysics 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 astrophysics. 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.