The interface to user data

 

The more complicated the data structure, the more urgent the question becomes of how the user is to supply the structures to the package. This question is particularly important in a parallel context.

The packages reviewed here have taken the following list of approaches to this problem.

• Fully internal, not directly accessible, data structures (basically object oriented programming). This approach is taken in Petsc (3.10), ParPre (3.8), and BlockSolve (3.2).

  The data structures here are only accessible through function calls. This means that the package has to supply routines for constructing the structures, for inspecting them, and for applying them.

• Prescribed, user supplied, data structures. This approach is taken in Aztec (3.1); it is available in PCG (3.9).

  Here the user has to construct the data structures, but the package supplies the product and solve routines.

• User supplied, arbitrary, data structures, with user supplied product and solve routines. This approach is available in PCG (3.9) and Petsc (3.10); the object-oriented package IML++ (3.5) can also be considered to use this approach.
• User defined data structures, not passed to the iterative method at all; product and solve operations are requested through a reverse communication interface.

  This approach is taken in PIM (3.11); it is also available in PCG (3.9).