论文标题

优化多级蒙特卡洛中的移位选择,用于晶格QCD中的断开图

Optimizing Shift Selection in Multilevel Monte Carlo for Disconnected Diagrams in Lattice QCD

论文作者

Whyte, Travis, Stathopoulos, Andreas, Romero, Eloy, Orginos, Kostas

论文摘要

在晶格QCD中,对物理信号的断开图贡献的计算是一项计算昂贵的任务。为了提取物理信号,必须按随机估算逆晶格狄拉克操作员的痕迹。由于随机估计器的方差通常很大,因此必须采用差异技术。多级蒙特卡洛(MLMC)方法通过利用估计器的望远镜序列来减少痕量估计器的方差。频率拆分是一种使用一系列偏移运算符的逆上的方法来估计逆晶格狄拉克运算符的轨迹,但是没有先验方法可以选择最小化多级跟踪估计成本的偏移。在本文中,我们提出了一个采样和插值方案,该方案能够预测基础时空晶格的位移下与频率分裂相关的方差。插值方案能够将方差预测到高精度,因此选择对应于痕量估计成本的最小值的变化。我们表明,使用选定的偏移分配的频率将在跨部通气中显示出显着的加速,并且这些偏移可用于同一合奏中的多种配置,而没有对性能的惩罚。

The calculation of disconnected diagram contributions to physical signals is a computationally expensive task in Lattice QCD. To extract the physical signal, the trace of the inverse Lattice Dirac operator, a large sparse matrix, must be stochastically estimated. Because the variance of the stochastic estimator is typically large, variance reduction techniques must be employed. Multilevel Monte Carlo (MLMC) methods reduce the variance of the trace estimator by utilizing a telescoping sequence of estimators. Frequency Splitting is one such method that uses a sequence of inverses of shifted operators to estimate the trace of the inverse lattice Dirac operator, however there is no a priori way to select the shifts that minimize the cost of the multilevel trace estimation. In this article, we present a sampling and interpolation scheme that is able to predict the variances associated with Frequency Splitting under displacements of the underlying space time lattice. The interpolation scheme is able to predict the variances to high accuracy and therefore choose shifts that correspond to an approximate minimum of the cost for the trace estimation. We show that Frequency Splitting with the chosen shifts displays significant speedups over multigrid deflation, and that these shifts can be used for multiple configurations within the same ensemble with no penalty to performance.

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