MPISCATTERV

MPI_Scatterv is an MPI collective communication operation that distributes a variable number of elements from a root process to all processes within a communicator. It extends MPI_Scatter by allowing different recipients to receive different counts of data, specified by the sender.

Signature and parameters: In C, int MPI_Scatterv(const void *sendbuf, const int *sendcounts, const int *displs, MPI_Datatype sendtype, void *recvbuf, int recvcount, MPI_Datatype recvtype, int root, MPI_Comm comm); For Fortran, a corresponding subroutine MPI_SCATTERV exists. The root process provides sendbuf, an array sendcounts of length equal to the number of processes, and an array displs indicating starting indices in the sendbuf for each recipient. All processes call the routine with the same comm and root. Each process provides a recvbuf with space for recvcount elements of type recvtype.

Semantics: Process i receives sendcounts[i] elements of type sendtype, taken from sendbuf starting at displs[i], and copies them into its recvbuf. The recvcount on each process should be at least the number of elements it is intended to receive (and is typically equal to sendcounts[i]). The operation is collective; all processes in the communicator participate and must agree on the root.

Notes: MPI_IN_PLACE can be used on some implementations to optimize the root’s data handling, but behavior varies and portability should be checked in the MPI standard being used. Typical usage involves preparing the per-process receive buffers according to the counts for each rank. See also MPI_Scatter, MPI_Gatherv, and MPI_Gather.