MPI_GATHERV and MPI_SCATTERV are the variable-message-size versions of MPI_GATHER and MPI_SCATTER. MPI_GATHERV extends the functionality of MPI_GATHER by changing the receive count from an integer to an integer array and providing a new argument displs(array). MPI_GATHERV allows a varying count of data from each process and allows some flexibility for where the gathered data is placed in the root as well. As a counterpart of MPI_GATHERV, MPI_SCATTERV is an extension of MPI_SCATTER in the same relationship as MPI_GATHERV is to MPI_GATHER. There is more information on this topic in the module MPI Collective Communication II.

C

FORTRAN

The variables for Gatherv are:

sbuf	starting address of send buffer,
scount	number of elements in send buffer,
stype	data type of send buffer elements,
rbuf	starting address of receive buffer,
rcount	array containing number of elements to be received from each process,
displs	array specifying the displacement relative to rbuf at which to place the incoming data from corresponding process,
rtype	data type of receive buffer,
root	rank of receiving process,
comm	group communicator.

Note: rbuf, rcount, rtype are significant for the root process only.

The variables for Scatterv are:

sbuf	address of send buffer,
scount	integer array specifying the number of elements to send to each process,
displs	array specifying the displacement relative to sbuf from which to take the data going out to the corresponding process,
stype	data type of send buffer elements,
rbuf	address of receive buffer,
rcount	number of elements in receive buffer,
rtype	data type of receive buffer elements,
root	rank of sending process,
comm	group communicator

Note: sbuf, scount, and stype are significant for root process only