  In most recent substructuring methods, a fundamental role is played by the
coarse space. For some of these methods (e.g. BDDC and FETI-DP), its definition
relies on a 'minimal' set of coarse nodes (sometimes called corners) which
assures invertibility of local subdomain problems and also of the global coarse
problem. This basic set is typically enhanced by enforcing continuity of
functions at some generalized degrees of freedom, such as average values on
edges or faces of subdomains. We revisit existing algorithms for selection of
corners. The main contribution of this paper consists of proposing a new
heuristic algorithm for this purpose. Considering faces as the basic building
blocks of the interface, inherent parallelism, and better robustness with
respect to disconnected subdomains are among features of the new technique. The
advantages of the presented algorithm in comparison to some earlier approaches
are demonstrated on three engineering problems of structural analysis solved by
the BDDC method.
