Mollification in strongly Lipschitz domains with application to continuous and discrete De Rham complex


We construct mollification operators in strongly Lipschitz domains that do not invoke non-trivial extensions, are LpL^p stable for any real number p[1,]p\in[1,\infty], and commute with the differential operators \nabla, ×\nabla{\times}, and \nabla{\cdot}. We also construct mollification operators satisfying boundary conditions and use them to characterize the kernel of traces related to the tangential and normal trace of vector fields. We use the mollification operators to build projection operators onto general H1H^1-, H(curl)\mathbf{H}(\text{curl})- and H(div)\mathbf{H}(\text{div})-conforming finite element spaces, with and without homogeneous boundary conditions. These operators commute with the differential operators \nabla, ×\nabla{\times}, and \nabla{\cdot}, are LpL^p-stable, and have optimal approximation properties on smooth functions

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