Collaborative Research: Advanced Parallel Computing Techniques with Applications to Computational Cosmology

该项目正在同时和协同地推进计算宇宙学和并行计算的最新发展。宇宙学的突破提高了我们对星系和行星形成的理解，这是由于该项目在并行计算方面取得的进展。拥有超过十万个强大处理器的并行机现在正在建造中。NSF广泛使用的TeraScale设施在2001年已经部署了3,000台处理器机器。与此同时，算法的进步使得以更快的速度解决问题成为可能。然而，算法的复杂性，再加上在如此大的机器上将它们并行化的困难，仍然阻碍着科学和工程的进步。这个项目探索了一种基于对象的方法，它简化了开发高效并行应用程序的过程。这种方法允许用户在应用程序域中的自然实体级别编写应用程序，而无需明确考虑哪些处理器将容纳这些实体并执行相关的计算。要实现这一点，“运行时系统”必须能够自动做出细粒度的资源分配决策。为实现这一目标，正在寻求并行计算的进展。具体地说，应用程序开发人员可以根据以几种风格化模式彼此通信的数百万个对象的集合来指定程序。此外，并行组件可以插入和退出正在运行的计算，并以灵活的方式彼此交换数据。在这个基础设施的基础上，这个项目正在构建一个框架，使构建“面向粒子”的并行程序变得容易。除了计算宇宙学，主要涉及将星系、暗物质、恒星、行星体和气体表示为粒子的模拟，这样的程序也被用于其他领域。该框架包含高效的并行算法，可以在数十亿个粒子的集合上运行，这些粒子分布在拥有数万个处理器的机器上。这些进展正被用于开展宇宙学的科学研究。由并行计算机提供动力的结构形成的大型、详细的模拟对于从宇宙学理论做出定量预测是必要的。通过计算星系和星系团形成的非线性引力和气体动力学，我们正在创建星系目录、X射线图和其他可直接与新的卫星和地面数据进行比较的可观测数据，从而约束宇宙学理论的参数。这些参数包括暗物质的数量和性质，任何暗能量的存在和状态方程，重子的总量，以及宇宙中初始功能的性质。类似的模拟研究正在被用来研究行星是如何从原太阳圆盘形成的，以便建立行星形成的从头算理论。通过该项目开发的软件正在向广大研究人员提供。此外，还可以通过网络下载或可视化仿真的研究结果。

This project is advancing the state of art in both computational cosmology and parallel computing simultaneously and synergetically. Breakthroughs in cosmology, which improve our understanding of the formation of galaxies and planets, are enabled by advances in parallel computing being made in this project. Parallel machines with over hundred thousand powerful processors are now being built. NSF's widely accessible TeraScale facilities have already deployed a 3,000 processor machine in 2001. At the same time algorithmic advances have made it possible to solve problems at a much faster rate. Yet the complexity of algorithms combined with the difficulty of parallelizing them on such large machines remains a hindrance to advances in Science and Engineering. This project explores an object based methodology that is simplifying the process of developing highly efficient parallel applications. This approach allows users to write applications at the level of natural entities in the application domain, without explicit regard to which processors will house such entities andcarry out associated computations. To make this possible, the "runtime system" must be able to make fine-grained resource allocation decisions automatically. Advances in parallel computing are being sought to that end. Specifically, application developers may specify a program in terms of a collection of millions of objects that communicate with each other in several stylized patterns. In addition, parallel components can be plugged in and out of running computations, and exchange data with each other in a exible manner. Based on this infrastructure, this project is building a framework that makes it easy to build "particle-oriented" parallel programs. In addition to computational cosmology, which predomi-nately involves simulations that represent galaxies, dark matter, stars, planetary bodies and gas as particles, such programs are used in other fields as well. The framework contains highly efficient parallel algorithms that operate on collections of billions of particles, spread across machines with tens of thousands of processors. These advances are being used to carry out scientific studies in cosmology. Large, detailed simulations of structure formation powered by parallel computers are necessary to make quantitative predictions from cosmological theories. By calculating the non-linear gravitational and gas dynamics of the formation of galaxies and clusters of galaxies, we are creating galaxy catalogues, X-ray maps, and other observables that can be compared directly with new satellite and ground-based data, and thereby constrain the parameters of cosmological theories. These parameters include the amount and nature of the dark matter, the existence and equation of state of any dark energy, the total amount of baryons, and the nature of the initial uctuations in the Universe. Similar simulation studies are being used to study how planets form from a proto-solar disk in order to create an ab initio theory of planet formation. The software developed via this project is being made available to a wide community of researchers. Also, the research results of simulations can be downloaded or visualized via the web.