Explain why all communication functions in MPI that deal with messages require a description of the message data type.

Pick three of the functions provided by MPI for collective communication, listed below, and explain what they do:

int MPI_Barrier (MPI_Comm comm);
int MPI_Bcast (void *buffer, ..., int root, MPI_Comm comm);
int MPI_Gather (void *sendbuf, void *recvbuf, ..., int root, MPI_Comm comm);
int MPI_Scatter (void *sendbuf, void *recvbuf, ..., int root, MPI_Comm comm);
int MPI_Alltoall (void *sendbuf, void *recvbuf, ..., int root, MPI_Comm comm);
int MPI_Reduce (void *sendbuf, void *recvbuf, ..., MPI_Op op, int root, MPI_Comm comm);
int MPI_Scan (void *sendbuf, void *recvbuf, ..., MPI_Op op, int root, MPI_Comm comm);