communicator, constructors The following are collective functions that are invoked by all processes in the group associated with comm.
MPI_Comm_dup(MPI_Comm comm, MPI_Comm *newcomm)
MPI_COMM_DUP(COMM, NEWCOMM, IERROR)INTEGER COMM, NEWCOMM, IERROR
MPI_COMM_DUP creates a new intracommunicator, newcomm, with the same fixed attributes (group, or groups, and topology) as the input intracommunicator, comm. The newly created communicators at the processes in the group of comm define a new, distinct communication domain, with the same group as the old communicators. The function can also be used to replicate intercommunicators.
The association of user-defined (or cached) attributes with
newcomm is controlled by the copy callback function
specified when the attribute was attached
to comm.
callback function, copy
For each key value, the respective
copy callback function determines the attribute value associated with
this key in the new communicator. User-defined attributes are
discussed in Section 
.
MPI_Comm_create(MPI_Comm comm, MPI_Group group, MPI_Comm *newcomm)
MPI_COMM_CREATE(COMM, GROUP, NEWCOMM, IERROR)INTEGER COMM, GROUP, NEWCOMM, IERROR
This function creates a new intracommunicator newcomm with communication group defined by group. No attributes propagates from comm to newcomm. The function returns MPI_COMM_NULL to processes that are not in group. MPI_COMM_NULL The communicators returned at the processes in group define a new intra-group communication domain.
The call is erroneous if not all group arguments have the same value on different processes, or if group is not a subset of the group associated with comm (but it does not have to be a proper subset). Note that the call is to be executed by all processes in comm, even if they do not belong to the new group.
MPI_Comm_split(MPI_Comm comm, int color, int key, MPI_Comm *newcomm)
MPI_COMM_SPLIT(COMM, COLOR, KEY, NEWCOMM, IERROR)INTEGER COMM, COLOR, KEY, NEWCOMM, IERROR
This function partitions the group associated with comm into disjoint subgroups, one for each value of color. Each subgroup contains all processes of the same color. Within each subgroup, the processes are ranked in the order defined by the value of the argument key, with ties broken according to their rank in the old group. A new communication domain is created for each subgroup and a handle to the representative communicator is returned in newcomm. A process may supply the color value MPI_UNDEFINED to not be a member of any new group, in which case newcomm returns MPI_COMM_NULL. This is a MPI_COMM_NULL collective call, but each process is permitted to provide different values for color and key. The value of color must be nonnegative.
A call to MPI_COMM_CREATE(comm, group, newcomm) is equivalent to
a call to
MPI_COMM_SPLIT(comm, color, key, newcomm), where all
members of group provide color
and
key
rank in
group, and all processes that are not members of
group provide
color MPI_UNDEFINED.
The function MPI_COMM_SPLIT allows
more general partitioning of a group
into one or more subgroups with optional reordering.
