Core MPI C syntax

All routines return an int error code, not shown here, except MPI_Wtime and MPI_Wtick. For more documentation and tutorials, see: MPI forum, IBM, Argonne, OpenMPI, NCSA, LLNL

Header file, startup, shutdown, timer

#include <mpi.h>

MPI_Init( &argc, &argv );
MPI_Comm_size( comm, &size );
MPI_Comm_rank( comm, &rank );
MPI_Finalize();
double time = MPI_Wtime();

Send and Receive

MPI_Send    ( sendbuf, sendcount, sendtype, dest,   sendtag, comm );
MPI_Isend   ( sendbuf, sendcount, sendtype, dest,   sendtag, comm, &request );
MPI_Sendrecv( sendbuf, sendcount, sendtype, dest,   sendtag,
              recvbuf, recvcount, recvtype, source, recvtag, comm, &status  );
MPI_Recv    ( recvbuf, recvcount, recvtype, source, recvtag, comm, &status  );
MPI_Irecv   ( recvbuf, recvcount, recvtype, source, recvtag, comm, &request );

Non-blocking completion

MPI_Wait    ( &request,        &status );
MPI_Test    ( &request, &flag, &status );
MPI_Waitall ( count, requests_array,        statuses_array );
MPI_Testall ( count, requests_array, &flag, statuses_array );
MPI_Waitsome( count, requests_array, &outcount, indices_array, statuses_array );
MPI_Testsome( count, requests_array, &outcount, indices_array, statuses_array );

Collective

MPI_Barrier       ( comm );
MPI_Bcast         ( buf,     count,     datatype, root, comm );
MPI_Scatter       ( sendbuf, sendcount, sendtype,
                    recvbuf, recvcount, recvtype, root, comm );
MPI_Alltoall      ( sendbuf, sendcount, sendtype,
                    recvbuf, recvcount, recvtype, comm );
MPI_Reduce        ( sendbuf, recvbuf, count,      datatype, op, root, comm );
MPI_Allreduce     ( sendbuf, recvbuf, count,      datatype, op, comm );
MPI_Reduce_scatter( sendbuf, recvbuf, recvcounts, datatype, op, comm );

Datatypes

void *buf, *sendbuf, *recvbuf;
int  count, outcount, sendcount, recvcount, recvcounts[N];
int  dest, source, root, rank, size, indices_array[N];
int  tag, sendtag, recvtag, flag;
MPI_Comm     comm, newcomm;
MPI_Request  request, requests_array[N];
MPI_Status   status,  statuses_array[N];
MPI_Datatype datatype, sendtype, recvtype;
MPI_Op       op;

Constants

// Communicators
MPI_COMM_WORLD
MPI_COMM_SELF

// Wildcards
MPI_ANY_SOURCE
MPI_ANY_TAG

// Options
MPI_IN_PLACE

// Datatypes, selected
MPI_CHAR
MPI_SIGNED_CHAR
MPI_INT
MPI_LONG
MPI_UNSIGNED_CHAR
MPI_UNSIGNED
MPI_UNSIGNED_LONG
MPI_FLOAT
MPI_DOUBLE
MPI_BYTE
MPI_PACKED

// Reduction operations
MPI_MAX
MPI_MIN
MPI_SUM
MPI_PROD
MPI_BAND (bitwise and)
MPI_BOR  (bitwise or )
MPI_BXOR (bitwise xor)
MPI_LAND (logical and)
MPI_LOR  (logical or )
MPI_LXOR (logical xor)
MPI_MAXLOC
MPI_MINLOC

MPI_Status

stat.MPI_SOURCE
stat.MPI_TAG
MPI_Get_count   ( &status, datatype, &count );

Cartesian grid

MPI_Dims_create ( nnodes, ndims, dims );
MPI_Cart_create ( comm,      ndims, dims, periods, reorder, comm_cart );
MPI_Cart_coords ( comm_cart, rank, maxdims, coords );  // map rank to coords
MPI_Cart_rank   ( comm_cart, coords, &rank );          // map coords to rank
MPI_Cart_shift  ( comm_cart, direction, disp, source, dest );

User-defined Types

MPI_Type_vector ( count, blocklength, stride, oldtype, &newtype );
MPI_Type_commit ( datatype );
MPI_Type_free   ( datatype );

Datatypes, in addition to first page

int nnodes, ndims, maxdims, reorder;
int dims[ndims], periods[ndims], coords[ndims];
MPI_Communicator comm_cart;
MPI_Datatype oldtype, newtype;

Copyright © 2011 by Mark Gates. Updated September 7, 2011. Available from http://web.eecs.utk.edu/~mgates3/ You may freely copy and modify this document under the Creative Commons Attribution license. When distributing, please include the above link and copyright for this original document.