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The MPI calls used by the MILC code: (Carleton)
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MPI_Init
MPI_Attr_get
MPI_Irecv
MPI_Issend
MPI_Send
MPI_Recv
MPI_Wait
MPI_Comm_rank
MPI_Comm_size
MPI_Barrier
MPI_Allreduce
MPI_Bcast
MPI_Abort
MPI_Finalize

Then, here is a brief list of the main components of the higher layer
communications primitives according to the MILC message passing model.
I haven't included broadcasts and variety of reduce operations, since
these are already implemented or easily implemented in the Columbia
Physics System.  These routines sit on top of MPI.  They are the
routines that we should replace in a more efficient port of the MILC
code to the QCDOC.

make_gather   Sets up neighbor lists for an arbitrary map of sites onto
              sites.  Of course, the most common map is to next
              neighbors.  The FFT needs a different map, of course.  A
              frequently used map is a simple displacement, for which
              there are specialized gather routines.  A number of
              applications use maps with an arbitray displacement.

start_gather  Initiates asynchronous communication according to the
              gather specified by make_gather.

wait_gather    Waits for asynchronous communication to complete.

cleanup_gather Frees storage for a completed gather.

restart_gather Same as start gather, but skips initialization.

send_field     Sends from one node to another.  Used particularly in I/O.
get_field      Receives from send_field.

There are also "field_pointer_at_coordinates" and
"field_pointer_at_direction" for fetching a single data item to a
given node, but they have fallen into disuse, so could probably be
omitted -- certainly in the first crack.