BPKIT is a toolkit of block preconditioners for the iterative solution of linear systems. The most effective general purpose and black-box type of preconditioners are available, including block SSOR, block tridiagonal ILU, and the block extension of point ILU with level-of-fill. Any of these "global" preconditioners may be coupled with one of a large collection of "local" preconditioners for approximately or exactly inverting or solving with the diagonal or pivot blocks. These include a number of approximate inverse techniques. By combining a global and local preconditioner, a wide variety of preconditionings are possible, matched to the difficulty and structure of the problem.
