mpi.get.sourcetag finds the source and tag of a received message.
mpi.get.sourcetag(status = 0)a status number
2 dim int vector. The first integer is the source and the second is the tag.
When mpi.any.source and/or mpi.any.tag are
used by mpi.recv or mpi.probe, one can use
mpi.get.sourcetag
to find who sends the message or with what a tag number.
mpi.get.sourcetag must be called immediately after calling
mpi.recv or mpi.probe otherwise the obtained information may not
be right.