Error analysis for a Crouzeix–Raviart approximation of the obstacle problem

In the present paper, we study a Crouzeix–Raviart approximation of the obstacle problem, which imposes the obstacle constraint in the midpoints ( i.e. , barycenters) of the elements of a triangulation. We establish a priori error estimates imposing natural regularity assumptions, which are optimal, and the reliability and efficiency of a primal-dual type a posteriori error estimator for general obstacles and involving data oscillation terms stemming only from the right-hand side. Numerical experiments are carried out to support the theoretical findings.