## Abstract

We consider the finite element solution of the vector Laplace equation on a domain in two dimensions. For various choices of boundary conditions, it is known that a mixed finite element method, in which the rotation of the solution is introduced as a second unknown, is advantageous, and appropriate choices of mixed finite element spaces lead to a stable, optimally convergent discretization. However, the theory that leads to these conclusions does not apply to the case of Dirichlet boundary conditions, in which both components of the solution vanish on the boundary. We show, by computational example, that indeed such mixed finite elements do not perform optimally in this case, and we analyze the suboptimal convergence that does occur. As we indicate, these results have implications for the solution of the biharmonic equation and of the Stokes equations using a mixed formulation involving the vorticity.

Original language | English (US) |
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Article number | 1250024 |

Journal | Mathematical Models and Methods in Applied Sciences |

Volume | 22 |

Issue number | 9 |

DOIs | |

State | Published - Sep 2012 |

### Bibliographical note

Funding Information:The work of the first author was supported in part by NSF grant DMS-1115291. The work of the second author was supported in part by NSF grant DMS-0910540. The work of the third author was supported in part by NSF grant DMS-1014817. This work was primarily carried out at the Institute for Mathematics and its Applications at the University of Minnesota where the authors were visiting.

## Keywords

- Hodge Laplacian
- Vector Laplacian
- mixed finite elements