The parallel implementation of GCR is addressed, with particular focus on communication costs associated with orthogonalization
processes. This consideration brings up questions concerning the use of Householder reflections with GCR. To precondition
the GCR method a block Gauss-Jacobi method is used. Approximate solvers are used to obtain a solution of the diagonal blocks.
Experiments on a cluster of HP workstations and on a Cray T3E are given.
Keywords approximate subdomain solution - parallel Krylov subspace methods - orthogonalization methods