# Surface Crouzeix-Raviart element for the Laplace-Beltrami equation

## TL;DR

This paper develops a surface Crouzeix-Raviart finite element method for the Laplace-Beltrami equation on approximated surfaces, establishing optimal error estimates and introducing a superconvergent gradient recovery technique validated by numerical experiments.

## Contribution

It introduces a novel surface Crouzeix-Raviart element for geometric PDEs and a superconvergent gradient recovery method using only discretization surface information.

## Key findings

- Optimal error estimates are established for the discretization.
- The superconvergent gradient recovery method is validated numerically.
- The method serves as an asymptotically exact a posteriori error estimator.

## Abstract

This paper is concerned with the nonconforming finite element discretization of geometric partial differential equations. In specific, we construct a surface Crouzeix-Raviart element on the linear approximated surface, analogous to a flat surface. The optimal error estimations are established even though the presentation of the geometric error. By taking the intrinsic viewpoint of manifolds, we introduce a new superconvergent gradient recovery method for the surface Crouzeix-Raviart element using only the information of discretization surface. The potential of serving as an asymptotically exact {\it a posteriori} error estimator is also exploited. A series of benchmark numerical examples are presented to validate the theoretical results and numerically demonstrate the superconvergence of the gradient recovery method.