Initializes or finalizes MPI.

Following a call to the function MP_SETUP(), the module MPI_node_int will contain information about the number of processors, the rank of a processor, the communicator for IMSL Fortran Numerical Library, and the usage priority order of the node machines:

INTEGER, ALLOCATABLE :: MPI_NODE_PRIORITY(:)

INTEGER, SAVE :: MP_LIBRARY_WORLD = huge(1)

LOGICAL, SAVE :: MPI_ROOT_WORKS = .TRUE.

INTEGER, SAVE :: MP_RANK = 0, MP_NPROCS = 1

When the function MP_SETUP() is called with no arguments, the following events occur:

When the generic function MP_SETUP(N) is called, where N is a positive integer, a call to MP_SETUP() is first made, using no argument. Use just one of these calls to MP_SETUP(). This initializes the MPI system and the other parameters described above. The array MPI_NODE_PRIORITY(:) is allocated with size MP_NPROCS. Then DOUBLE PRECISION matrix products C = AB, where A and B are N by N matrices, are computed at each node and the elapsed time is recorded. These elapsed times are sorted and the contents of MPI_NODE_PRIORITY(:) are permuted in accordance with the shortest times yielding the highest priority. All the nodes in the communicator MP_LIBRARY_WORLD are timed. The array MPI_NODE_PRIORITY(:) is then broadcast from the root to the remaining nodes of MP_LIBRARY_WORLD using the routine MPI_Bcast(). Timing matrix products to define the node priority is relevant because the effort to compute C is comparable to that of many linear algebra computations of similar size. Users are free to define their own node priority and broadcast the array MPI_NODE_PRIORITY(:) to the alternate nodes in the communicator.

To print any IMSL Fortran Numerical Library error messages that have occurred at any node, and to finalize MPI, use the function call MP_SETUP(‘Final’). The case of the string ‘Final’ is not important. Any error messages pending will be discarded after printing on the root node. This is triggered by popping the name ‘MP_SETUP’ from the subprogram stack or returning to Level 1 in the stack. Users can obtain error messages by popping the stack to Level 1 and still continuing with MPI calls. This requires executing call e1pop (‘MP_SETUP’). To continue on after summarizing errors execute call e1psh (‘MP_SETUP’). More details about the error processor are found in Reference Material chapter of this manual.

Messages are printed by nodes from largest rank to smallest, which is the root node. Use of the routine MPI_Finalize() is made within MP_SETUP(‘Final’), which shuts down MPI. After MPI_Finalize() is called, the value of MP_NPROCS = 0. This flags that MPI has been initialized and terminated. It cannot be initialized again in the same program unit execution. No MPI routine is defined when MP_NPROCS has this value.

Here an alternate node is used to compute the majority of a single application, and the user does not need to make any explicit calls to MPI routines. The time-consuming parts are the evaluation of the eigenvalue-eigenvector expansion, the solving step, and the residuals. To do this, the rank‑2 arrays are changed to a box data type with a unit third dimension. This uses parallel computing. The node priority order is established by the initial function call, MP_SETUP(n). The root is restricted from working on the box data type by assigning MPI_ROOT_WORKS=.false.. This example anticipates that the most efficient node, other than the root, will perform the heavy computing. Two nodes are required to execute.