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arXiv 1604.08057hep-lat
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计算大型复矩阵函数导数的数值方法及其在有限化学势下重叠Dirac算子中的应用

A numerical method to compute derivatives of functions of large complex matrices and its application to the overlap Dirac operator at finite chemical potential

M. Puhr, P. V. Buividovich

摘要:

给出了一般复矩阵函数导数的数值计算方法。该方法可以与评估或近似期望的矩阵函数的任何算法结合使用,特别是与隐式Krylov-Ritz型近似结合使用。该方法的一个重要用例是在有限化学势下计算晶格量子色动力学(QCD)中的重叠狄拉克算子,这需要将非厄米矩阵的符号函数应用于某些源向量。虽然非厄米矩阵的符号函数在实践中不能用源无关多项式或有理函数有效地近似,但是仍然可以为每个特定的源向量构造足够好的近似多项式。我们的方法允许一个有效的计算的衍生物的这种隐式近似相对于规范场或其他外部参数,这是必要的计算守恒的晶格电流或费米子力的混合蒙特卡罗或朗之万模拟。我们还给出了一个明确的紧缩处方的情况下,当一个知道几个特征值和特征向量的矩阵的微分函数的论点。我们测试的方法为双边Lanczos近似的有限密度重叠狄拉克运营商的实际$SU(3)$规范场配置的大小为$14\times14^3$和$6\times18^3$格点。

英文摘要:

We present a method for the numerical calculation of derivatives of functions of general complex matrices. The method can be used in combination with any algorithm that evaluates or approximates the desired matrix function, in particular with implicit Krylov-Ritz-type approximations. An important use case for the method is the evaluation of the overlap Dirac operator in lattice Quantum Chromodynamics (QCD) at finite chemical potential, which requires the application of the sign function of a non-Hermitian matrix to some source vector. While the sign function of non-Hermitian matrices in practice cannot be efficiently approximated with source-independent polynomials or rational functions, sufficiently good approximating polynomials can still be constructed for each particular source vector. Our method allows for an efficient calculation of the derivatives of such implicit approximations with respect to the gauge field or other external parameters, which is necessary for the calculation of conserved lattice currents or the fermionic force in Hybrid Monte-Carlo or Langevin simulations. We also give an explicit deflation prescription for the case when one knows several eigenvalues and eigenvectors of the matrix being the argument of the differentiated function. We test the method for the two-sided Lanczos approximation of the finite-density overlap Dirac operator on realistic $SU(3)$ gauge field configurations on lattices with sizes as large as $14\times14^3$ and $6\times18^3$.

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