We consider an additive Vanka-type smoother for the Poisson equation discretized by the standard finite difference centered scheme. Using local Fourier analysis, we derive analytical formulas for the optimal smoothing factors for two types of smoothers, called vertex-wise and element-wise Vanka smoothers, and present the corresponding stencils. Interestingly, in one dimension the element-wise Vanka smoother is equivalent to the scaled mass operator obtained from the linear finite element method, and in two dimensions the element-wise Vanka smoother is equivalent to the scaled mass operator discretized by bilinear finite element method plus a scaled identity operator. Based on these discoveries, the mass matrix obtained from finite element method can be used as an approximation to the inverse of the Laplacian, and the resulting mass-based relaxation scheme features small smoothing factors in one, two, and three dimensions. Advantages of the mass operator are that the operator is sparse and well conditioned, and the computational cost of the relaxation scheme is only one matrix-vector product; there is no need to compute the inverse of a matrix. These findings may help better understand the efficiency of additive Vanka smoothers and develop fast solvers for numerical solutions of partial differential equations.
翻译:我们认为Poisson 方程式的添加型Vanka型光滑剂是用标准限值偏差法分解的。 使用本地的 Fleier 分析,我们为两种类型的平滑器(称为顶点和元素-Vanka平滑器)得出最佳平滑因素的分析公式,并展示相应的平滑剂。 有趣的是,在一个层面,从元素角度的Vanka平滑器相当于从线性有限元素法中获得的按比例质量操作器,在两个层面,从元素-偏滑器相当于通过双线性有限元素法和比例化身份操作器分解的大规模操作器。 基于这些发现,从有限元素法获得的质量矩阵可以用作向拉普拉卡反面的近光度,而由此产生的大规模放松方案则以一、二和三个维度小的平滑动因素为特征。 质量操作器的优点是操作器的操作器十分稀少且条件良好,而宽松计划的计算成本仅相当于一个矩阵- 量控制器产品; 不需要根据这些发现, 从有限要素方法获得的定性矩阵矩阵矩阵矩阵矩阵矩阵矩阵, 来对一个快速的解决方案进行反分析。 这些结果可能更能更清楚地理解平差变的公式。