A call of the form MPI_SEND(buf, count, datatype , ...), where count > 1 , is interpreted as if the call was passed a new datatype which is the concatenation of count copies of datatype. Thus, MPI_SEND(buf, count, datatype, dest, tag, comm) is equivalent to,
MPI_TYPE_CONTIGUOUS(count, datatype, newtype) MPI_TYPE_COMMIT(newtype) MPI_SEND(buf, 1, newtype, dest, tag, comm).
Similar statements apply to all other communication functions that have a count and datatype argument.