MPICommcreate

MPI_Comm_create is a function in the Message Passing Interface (MPI) library that creates a new communicators from an existing communicator. This function is used to duplicate an existing communicator, allowing multiple processes to communicate with each other independently.

The function takes two arguments: communicator and group. The communicator argument is the existing communicator that is to be duplicated, and the group argument is the set of ranks that will make up the new communicator. The function returns a new communicator, which is not connected to the original communicator.

The new communicator communicates only with the ranks specified in the group argument, and does not recognize any new processes that may have joined the system after the group was defined. The results of any collective operations performed on the new communicator will not be communicated to the original communicator.

This function can be used in a variety of situations, including when multiple independent simulations are to be run on the same system, or when a group of processes needs to be isolated from the rest of the system.

It is worth noting that a new group is created with each call to MPI_Comm_create. The processes belonging to the original group remain in that group. Creating a new communicator does not affect the members of the original group. All members of the original group remain connected to each other, even after the new communicator has been created.