| MPI_EXSCAN(sendbuf, recvbuf, count, datatype, op, comm) | |
| IN sendbuf | starting address of send buffer (choice) |
| OUT recvbuf | starting address of receive buffer (choice) |
| IN count | number of elements in input buffer (non-negative integer) |
| IN datatype | data type of elements of input buffer (handle) |
| IN op | operation (handle) |
| IN comm | intracommunicator (handle) |
int MPI_Exscan(const void* sendbuf, void* recvbuf, int count, MPI_Datatype datatype, MPI_Op op, MPI_Comm comm)
MPI_Exscan(sendbuf, recvbuf, count, datatype, op, comm, ierror)
TYPE(*), DIMENSION(..), INTENT(IN) :: sendbuf
TYPE(*), DIMENSION(..) :: recvbuf
INTEGER, INTENT(IN) :: count
TYPE(MPI_Datatype), INTENT(IN) :: datatype
TYPE(MPI_Op), INTENT(IN) :: op
TYPE(MPI_Comm), INTENT(IN) :: comm
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
MPI_EXSCAN(SENDBUF, RECVBUF, COUNT, DATATYPE, OP, COMM, IERROR)
<type> SENDBUF(*), RECVBUF(*)
INTEGER COUNT, DATATYPE, OP, COMM, IERROR
If comm is an intracommunicator, MPI_EXSCAN is used to perform a prefix reduction on data distributed across the group. The value in recvbuf on the process with rank 0 is undefined, and recvbuf is not signficant on process 0. The value in recvbuf on the process with rank 1 is defined as the value in sendbuf on the process with rank 0. For processes with rank i > 1, the operation returns, in the receive buffer of the process with rank i, the reduction of the values in the send buffers of processes with ranks 0,...,i-1 (inclusive). The routine is called by all group members using the same arguments for count, datatype, op and comm, except that for user-defined operations, the same rules apply as for MPI_REDUCE. The type of operations supported, their semantics, and the constraints on send and receive buffers, are as for MPI_REDUCE.
The ``in place'' option for intracommunicators is specified by passing MPI_IN_PLACE in the sendbuf argument. In this case, the input data is taken from the receive buffer, and replaced by the output data. The receive buffer on rank 0 is not changed by this operation.
This operation is invalid for intercommunicators.
Rationale.
The exclusive scan is more general than the inclusive scan.
Any inclusive scan operation can be
achieved by using the exclusive scan and then locally combining the
local contribution. Note that for non-invertable operations such as
MPI_MAX, the exclusive scan cannot be computed with the
inclusive scan.
( End of rationale.)