FRG: Collaborative Research: Error Quantification and Control for Gravitational Waveform Simulation

该项目的目的是开发实用的严格方法，以可靠的精度估计引力波模拟计算波形的误差，以支持NSF资助的激光干涉仪引力观测站（LIGO）。 该项目汇集了一组具有偏微分方程解的误差估计构建专长的应用和计算数学家，以及具有爱因斯坦方程数值解和引力波数据分析专长的物理学家。 主要的技术目标是开发和分析新的数学和计算方法，这些方法可以被引力物理学界用来计算爱因斯坦方程数值解的误差以及由此确定的引力波形的严格和可靠的准确估计。 具体而言，本研究探讨了以下问题：（1）使用伴随灵敏度技术的误差量化和后验分析及其相关的数值实现：（2）由目标导向误差控制驱动的自适应算法及其相关的理论收敛性分析;（3）协方差对称性和相关几何结构在误差分析和数值方法构造中的作用。作为后验分析的一部分，项目组将发展爱因斯坦方程的伴随算子和对偶的基本理论。这将为今后利用LIGO数据进行敏感性分析、数据同化和不确定性量化等研究奠定基础。应该强调的是，拟议研究的主要目标是离散化中性的，因此对现有的数值相对论代码的广度具有广泛的适用性。NSF支持的激光干涉仪引力天文台（LIGO）只有在高精度的引力波形模型可用作数据分析过程的一部分时才能成功，既用于探测引力波，也用于测量任何探测到的信号的物理特性。 最强的引力波源预计是重的，致密的恒星或黑洞之间的碰撞，这只能使用复杂的数值模拟来精确建模，以计算预期的引力波形。 需要这样的波形来构造允许在有噪声的检测器中检测弱引力波信号的滤波器，并且还需要这样的波形来测量任何检测到的信号的源的物理特性。 完成所需数据分析任务所需的波形精度相当高。 然而，数值相对论社区还没有开发出分析和计算工具，需要严格评估的数值波形模型的准确性。 如果数值相对论社区目前使用的定性精度测量过于乐观，那么该项目开发的严格的新方法可能会决定LIGO的成功与失败。 如果目前的数值波形实际上足够准确，则本项目开发的方法可以提高确定具有指定精度水平的波形的计算效率，从而降低生产成本。

The purpose of this project is to develop practical rigorous methods for estimating the error in computed waveforms from gravitational wave simulation with reliable accuracy, in support of the NSF-funded Laser Interferometer Gravitational Observatory (LIGO). The project brings together a team of applied and computational mathematicians with expertise in constructing error estimates for solutions of partial differential equations and physicists with expertise in numerical solutions of the Einstein equation and gravitational wave data analysis. The primary technical goal is to develop and analyze new mathematical and computational methods that can be used by the gravitational physics community to compute rigorous and reliably accurate estimates for the errors of numerical solutions of the Einstein equations and the gravitational waveforms that are determined from them. In particular, this research explores the following issues:(1) Error quantification and a posteriori analysis using adjoint sensitivity techniques, and their associated numerical implementation;(2) Adaptive algorithms that are driven by goal-oriented error control, and their associated theoretical convergence analysis; and(3) The role of covariance symmetry and associated geometric structures in error analysis and the construction of numerical methods.As part of the a posteriori analysis, the project team will develop the basic theory of adjoint operators and duality for the Einstein equations. This will provide the foundation for future investigations into sensitivity analysis, data assimilation and uncertainty quantification for using LIGO data. It should be emphasized that the main thrusts of the proposed research are discretization-neutral, and therefore have broad applicability to the breadth of numerical relativity codes in existence.The NSF-supported Laser Interferometer Gravitational Observatory (LIGO) can be successful only if highly accurate gravitational waveform models are available for use as part of the data analysis process, both for detecting gravitational waves and also for measuring the physical properties of any detected signals. The strongest sources of gravitational waves are expected to be collisions between heavy, dense stars or black holes, which can only be modeled accurately using complex numerical simulations to calculate the anticipated gravitational waveforms. Such waveforms are needed to construct the filters that allow detection of the weak gravitational-wave signals in the noisy detector, and such waveforms are also needed to measure the physical properties of the sources of any detected signals. The waveform accuracy needed to accomplish the required data analysis tasks is quite high. However, the numerical relativity community has yet to develop the analytic and computational tools needed to evaluate rigorously the accuracy of the numerical waveform models. If the qualitative accuracy measures currently used by the numerical relativity community are too optimistic, the rigorous new methods developed by this project could make the difference between success and failure of LIGO. If the current numerical waveforms are in fact accurate enough, the methods developed by this project could improve the computational efficiency of determining waveforms with a specified accuracy level, and thus reduce the cost of producing them.