arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2004.12778math.AP
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Friedrichs型系统的适定变分形式

Well-posed variational formulations of Friedrichs-type systems

Martin Berggren, Linus Hägg

摘要:

所有有限元法,以及希尔伯特空间理论的偏微分方程,依赖于变分公式,也就是说,问题的类型:找到$u\in V$使得$a(v,u) = l(v)$对于每个$v\in L$,其中$V, L$是Sobolev空间。然而,对于弗里德里希类型的系统,有一个鲜明的差距之间建立的适定性理论,这是不是变分的,和非常成功的不连续伽辽金方法,已开发的这种系统,这是变分的。在试图推翻这种二分法,我们提出,通过三个具体的例子,越来越复杂,适定的变分公式的边界和初始-边值问题的弗里德里希类型。我们介绍的变分形式是那些用于不连续Galerkin方法的推广,在这个意义上,非齐次边界和初始条件是强制执行弱通过积分的变分形式。在我们介绍的变分形式中,解空间被定义为与所讨论的微分算子相关联的图空间的子空间$V$,而测试函数空间$L$是$L^2$空间的元组,这些空间分别执行方程、特征类型的边界条件和初始条件。

英文摘要:

All finite element methods, as well as much of the Hilbert-space theory for partial differential equations, rely on variational formulations, that is, problems of the type: find $u\in V$ such that $a(v,u) = l(v)$ for each $v\in L$, where $V, L$ are Sobolev spaces. However, for systems of Friedrichs type, there is a sharp disparity between established well-posedness theories, which are not variational, and the very successful discontinuous Galerkin methods that have been developed for such systems, which are variational. In an attempt to override this dichotomy, we present, through three specific examples of increasing complexity, well-posed variational formulations of boundary and initial--boundary-value problems of Friedrichs type. The variational forms we introduce are generalizations of those used for discontinuous Galerkin methods, in the sense that inhomogeneous boundary and initial conditions are enforced weakly through integrals in the variational forms. In the variational forms we introduce, the solution space is defined as a subspace $V$ of the graph space associated with the differential operator in question, whereas the test function space $L$ is a tuple of $L^2$ spaces that separately enforce the equation, boundary conditions of characteristic type, and initial conditions.

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