Mortar methods

Summary

Mortar methods are finite element discretizations on a domain cut into subdomains whose meshes need not match across the interfaces. Continuity across an interface is not imposed point by point but weakly. The jump must be orthogonal to a space of multiplier functions, the mortar space. They let each subdomain use its own mesh and polynomial degree while keeping optimal error estimates. This makes them a standard tool of domain decomposition methods.