Appendix

Here is an abbreviated reference of the features of mpi4py. For a full documentation of the API, see http://mpi4py.scipy.org/docs/apiref/.

Note

One of the main differences between this presentation of mpi4py and MPI in C or Fortan, besides being array-based, is that mpi4py is largely object oriented. The MPI Communicator in mpi4py is a Python class and MPI functions like Send or Broadcast are instance methods of the communicator class. The object-oriented nature of mpi4py is seen mostly in dealing with MPI topologies. I will not discuss these in detail, but rather focus on an introduction to the basics of distributed memory programming with MPI. Throughout the tutorial you will see functions like Send(...) presented as Comm.Send(...) where it is implied that Comm is an instance of the Comm class. I will document Comm as in input paramter to the function.

Instance Methods of Comm Class

For full documentation of the Comm class, see http://mpi4py.scipy.org/docs/apiref/mpi4py.MPI.Comm-class.html.

“Uppercase” Communication

Abort( errorcode=0)

Terminate MPI execution environment

Allgather(sendbuf, recvbuf)

Gather to All, gather data from all processes and distribute it to all other processes in a group

Allgatherv(sendbuf, recvbuf)

Gather to All Vector, gather data from all processes and distribute it to all other processes in a group providing different amount of data and displacements

Allreduce(sendbuf, recvbuf, Op op=SUM)

All Reduce

Alltoall(sendbuf, recvbuf)

All to All Scatter/Gather, send data from all to all processes in a group

Alltoallv(sendbuf, recvbuf)

All to All Scatter/Gather Vector, send data from all to all processes in a group providing different amount of data and displacements

Alltoallw(sendbuf, recvbuf)

Generalized All-to-All communication allowing different counts, displacements and datatypes for each partner

Barrier()

Barrier synchronization

Bcast(buf, root=0)

Broadcast a message from one process to all other processes in a group

Bsend(buf, dest=0, tag=0)

Blocking send in buffered mode

Bsend_init(buf, dest=0, tag=0)

Persistent request for a send in buffered mode

Call_errhandler(errorcode)

Call the error handler installed on a communicator

Clone()

Clone an existing communicator

Compare(type cls, Comm comm1, Comm comm2)

Compare two communicators

Disconnect()

Disconnect from a communicator

Free()

Free a communicator

Gather(sendbuf, recvbuf, root=0)

Gather together values from a group of processes

Gatherv(sendbuf, recvbuf, root=0)

Gather Vector, gather data to one process from all other processes in a group providing different amount of data and displacements at the receiving sides

Get_attr(keyval)

Retrieve attribute value by key

Get_errhandler()

Get the error handler for a communicator

Get_group()

Access the group associated with a communicator

Get_name()

Get the print name for this communicator

Get_parent(type cls)

Return the parent intercommunicator for this process

Get_rank()

Return the rank of this process in a communicator

Get_size()

Return the number of processes in a communicator

Get_topology()

Determine the type of topology (if any) associated with a communicator

Ibsend(buf, dest=0, tag=0)

Nonblocking send in buffered mode

Iprobe(source=0, tag=0, Status status=None)

Nonblocking test for a message

Irecv(buf, source=0, tag=0)

Nonblocking receive

Irsend(buf, dest=0, tag=0)

Nonblocking send in ready mode

Is_inter()

Test to see if a comm is an intercommunicator

Is_intra()

Test to see if a comm is an intracommunicator

Isend(buf, dest=0, tag=0)

Nonblocking send

Issend(buf, dest=0, tag=0)

Nonblocking send in synchronous mode

Join(type cls, fd)

Create a intercommunicator by joining two processes connected by a socket

Probe(source=0, tag=0, Status status=None)

Blocking test for a message

Recv(buf, source=0, tag=0, Status status=None)

Blocking receive

Recv_init(buf, source=0, tag=0)

Create a persistent request for a receive

Reduce(sendbuf, recvbuf, Op op=SUM, root=0)

Reduce

Reduce_scatter(sendbuf, recvbuf, recvcounts=None, Op op=SUM)

Reduce-Scatter (vector version)

Reduce_scatter_block(sendbuf, recvbuf, Op op=SUM)

Reduce-Scatter Block (regular, non-vector version)

Rsend(buf, dest=0, tag=0)

Blocking send in ready mode

Rsend_init(buf, dest=0, tag=0)

Persistent request for a send in ready mode

Scatter(sendbuf, recvbuf, root=0)

Scatter Vector, scatter data from one process to all other processes in a group

Scatterv([choice sendbuf, tuple_int sendcounts, tuple_int displacements, MPI_Datatype sendtype], choice recvbuf, root=0)

Scatter data from one process to all other processes in a group providing different amount of data and displacements at the sending side

Send(buf, dest=0, tag=0)

Blocking send

Send_init(buf, dest=0, tag=0)

Create a persistent request for a standard send

Sendrecv(sendbuf, dest=0, sendtag=0, recvbuf=None, source=0, recvtag=0, Status status=None)

Send and receive a message

Sendrecv_replace(buf, dest=0, sendtag=0, source=0, recvtag=0, Status status=None)

Send and receive a message

Set_errhandler(Errhandler errhandler)

Set the error handler for a communicator

Set_name(name)

Set the print name for this communicator

Ssend(buf, dest=0, tag=0)

Blocking send in synchronous mode

Ssend_init(buf, dest=0, tag=0)

Persistent request for a send in synchronous mode

“Lowercase” Communication

allgather(sendobj=None, recvobj=None)

Gather to All

allreduce(sendobj=None, recvobj=None, op=SUM)

Reduce to All

alltoall(sendobj=None, recvobj=None)

All to All Scatter/Gather

barrier()

Barrier

bcast(obj=None, root=0)

Broadcast

bsend(obj=None, dest=0, tag=0)

Send in buffered mode

gather(sendobj=None, recvobj=None, root=0)

Gather

ibsend(obj=None, dest=0, tag=0)

Nonblocking send in buffered mode

isend(obj=None, dest=0, tag=0)

Nonblocking send

issend(obj=None, dest=0, tag=0)

Nonblocking send in synchronous mode

recv(obj=None, source=0, tag=0, Status status=None)

Receive

reduce(sendobj=None, recvobj=None, op=SUM, root=0)

Reduce

scatter(sendobj=None, recvobj=None, root=0)

Scatter

send(obj=None, dest=0, tag=0)

Send

sendrecv(sendobj=None, dest=0, sendtag=0, recvobj=None, source=0, recvtag=0, Status status=None)

Send and Receive

ssend(obj=None, dest=0, tag=0)

Send in synchronous mode

The Op Class (Reduction Operations)

Within the Op class are values that represent predefine operations to be used with the “reduce” functions. There are also methods that allow the creation of user-defined operations. I present here a table of the predefined operations. Full documentation is found here: http://mpi4py.scipy.org/docs/apiref/mpi4py.MPI.Op-class.html

Name	Meaning
MPI.MAX	maximum
MPI.MIN	minimum
MPI.SUM	sum
MPI.PROD	product
MPI.LAND	logical and
MPI.BAND	bit-wise and
MPI.LOR	logical or
MPI.BOR	bit-wise or
MPI.LXOR	logical xor
MPI.BXOR	bit-wise xor
MPI.MAXLOC	max value and location
MPI.MINLOC	min value and location