Introduction

This document describes the routines or operators available in the PMDB runtime library. PMDB executes a copy of MDB in SPMD mode on each processor and provides the following categories of procedures to manipulate, manage, and provide information about the distributed mesh:

• Mesh loading and partitioning routines read in meshes stored in files and distribute them onto the processors. The meshes can either be already partitioned in which case they are read in parallel, or they can be partitioned after they are loaded on processor(s).
• Geometric model operators initializes up the correspondence between the addresses of geometric entities and their geometric model identification tags. This needs to done by PMDB since when the geometric model is loaded on each processor, mesh entities point to the addresses of geometric entities as part of their classification.
• Query routines return information related to the entities which are shared between processors. A rich set of queries about processor adjacency, and links to other shared entities are supported.
• Update routines provide the operators with which the shared entities and their links accross the processors can be manipulated. If the mesh is not changed by an application, then there is no need to use these routines.
• Gather/scatter maps are no longer supported, as the node structures are gone as of mesh 4.x.
• Mesh Migration routines enable entities to be redistributed in an unrestrictive manner. In addition, applications which use routines such as load balancing or just need to migrate entities among processors needs a mechanism whereby user specific data should also be migrated together with the entities. For example, adaptive finite element programs may store solution or elemental matrices on entities. The stored data may be irregular - e.g. p-adaptive methods may need to store vectors of different length on each entity. PMDB provides operators which users can call to register attached data by its tag and its storage size. Any entity which is migrated and which has data identified with a registered tag will also have its data migrated and attached automatically after reaching the destination processor. The mesh migration routines also support the new callback operations. If a "MigrateIn" or "MigrateOut" callback is attached, the callback will be called before an entity is packed to be migrated, or after it is unpacked after being migrated.
• Load balancing may be needed after refinement or coarsening is performed. PMDB provides an iterative scheme which balances the number of elements on each processor. Other load balancers are available which use the PMDB interface but which are not part of PMDB. Please see the documentaion on the OCTPART, ribPart, and ParMetis documentation for more information.
• Visualization: These routines provide IBM data explorer output to aid in visualization of partitioned meshes.

The following types are used and are described in detail in the SCOREC MDB manual [].

• pEntity a generic entity which can be region, face edge or vertex.
• eType: represents the type of the entity. It can be any one of Tvertex, Tedge, Tface, or Tregion.

Throughout manual the variable names given below appear extensively as parameters to library routines:

• num_of_procs : total number of processors used.
• pid: processor id.

Figure presents an example code of how PMDB library can be used to load and partition a mesh using orthogonal bisection. The code presents a standard template of calls to load and distribute a mesh over processors. The call to pmdb_ortho_rb() can be replaced with any other mesh loading or partitioning routines described in section . The call to do_something() can be replaced with code that uses the library routines presented in this manual.