Clusters: Full Configuration Interaction.

Another application comes from the area of computational chemistry. This application fits best into the shared-memory model, in that a global data structure is both read and updated in random patterns by all of the processes. Using p4's cluster model, we ported this program to a collection of four 25-processor Alliant FX/2800's connected by a HiPPI switch. That is, processes on a single cluster (one 25-processor Alliant) used monitors to coordinate access to their part of the shared data and to schedule themselves (using p4_askfor). Data in other clusters was accessed by sending messages to a data-manager process in that cluster. Again, p4's portability made it possible to develop the program on a single Sequent Symmetry (procgroup options allow the partitioning of a single shared-memory machine into several that communicate via messages) before running it on a set of Alliants connected by the HiPPI switch.