HPDDM is an efficient implementation of various domain decomposition methods
(DDM) such as one- and two-level Restricted Additive Schwarz (RAS) methods, the
Finite Element Tearing and Interconnecting (FETI) method, and the Balancing
Domain Decomposition (BDD) method. These methods can be enhanced with deflation
vectors computed automatically by the framework using:

- Generalized Eigenvalue problems on the Overlap (GenEO), an approach first
  introduced in a paper by Spillane et al., or
- local Dirichlet-to-Neumann operators, an approach first introduced in a paper
  by Nataf et al. and revisited by Conen et al.