NAME

       MPIL_Comm_gps  -   LAM/MPI-specific  function  to  return  the  GPS  information  of  a given rank from a
       communicator

SYNOPSIS

       #include <mpi.h>
       int MPIL_Comm_gps(MPI_Comm comm, int rank, int *pnid,
                        int *ppid)

INPUT PARAMETERS

       comm   - communicator (handle)
       rank   - rank of process to query (integer)

OUTPUT PARAMETERS

       pnid   - LAM node ID
       ppid   - LAM process ID

NOTES

       In the LAM implementation of MPI, each communicator has an integer context  ID  associated  with  it  for
       synchronizing on different contexts.  This ID is global to all the processes in the communicator's group,
       and  uniquely  identifies  that  communicator  for each process.  These properties allow the processes to
       safely exchange messages without interference from operations on other communicators.

       The MPI standard does not provide a way  to  access/view  this  implementation-dependent  synchronization
       since communicators are opaque objects.  Users do not need such access for normal MPI operations.  On the
       other  hand,  when  debugging  MPI  applications,  the  opaque nature of communicators hinders the user's
       efforts.  This is especially true on fully observable systems such as LAM, where users  can  monitor  the
       full state of the processes and message queues, which includes the context ID (see mpitask (1) and mpimsg
       (1)).

       LAM  supplementary  functions  do  not  operate  with  communicators and ranks but with nodes and process
       identifiers.  MPIL_Comm_gps accepts the MPI values and returns  the  LAM  values.   In  the  case  of  an
       intercommunicator the values returned are those of the process with the given rank in the remote group.

       This  is  a LAM/MPI-specific function and is intended mainly for debugging.  If this function is used, it
       should be used in conjunction with the LAM_MPI C preprocessor macro

       #if LAM_MPI
       int nid, pid;
       MPIL_Comm_gps(MPI_COMM_WORLD, 0, &nid, &pid);
       #endif

NOTES FOR FORTRAN

       All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK ) have an additional argument ierr at the
       end of the argument list.  ierr is an integer and has the same meaning as the return value of the routine
       in C.  In Fortran, MPI routines are subroutines, and are invoked with the call statement.

       All MPI objects (e.g., MPI_Datatype , MPI_Comm ) are of type INTEGER in Fortran.

ERRORS

       If an error occurs in an MPI function, the current MPI error handler is called to handle it.  By default,
       this error handler aborts the MPI job.  The error handler may be changed with  MPI_Errhandler_set  ;  the
       predefined  error  handler  MPI_ERRORS_RETURN  may be used to cause error values to be returned (in C and
       Fortran; this error handler is less useful in with the C++ MPI bindings.  The  predefined  error  handler
       MPI::ERRORS_THROW_EXCEPTIONS  should be used in C++ if the error value needs to be recovered).  Note that
       MPI does not guarantee that an MPI program can continue past an error.

       All MPI routines (except MPI_Wtime and MPI_Wtick ) return an error value; C routines as the value of  the
       function and Fortran routines in the last argument.  The C++ bindings for MPI do not return error values;
       instead,  error  values  are  communicated  by  throwing  exceptions  of  type MPI::Exception (but not by
       default).  Exceptions are only thrown if the error value is not MPI::SUCCESS .

       Note that if the MPI::ERRORS_RETURN handler is set in C++, while MPI functions will return upon an error,
       there will be no way to recover what the actual error value was.
       MPI_SUCCESS
              - No error; MPI routine completed successfully.
       MPI_ERR_COMM
              - Invalid communicator.  A common error is to use a null communicator in a call (not even  allowed
              in MPI_Comm_rank ).
       MPI_ERR_RANK
              - Invalid source or destination rank.  Ranks must be between zero and the size of the communicator
              minus  one;  ranks  in  a  receive  (  MPI_Recv  ,  MPI_Irecv  ,  MPI_Sendrecv , etc.) may also be
              MPI_ANY_SOURCE .

       MPI_ERR_ARG
              - Invalid argument.  Some argument is invalid and is not identified by  a  specific  error  class.
              This is typically a NULL pointer or other such error.

SEE ALSO

       MPIL_Comm_id, MPIL_Type_id

LOCATION

       mpil_id.c

LAM/MPI 7.1.4                                       6/24/2006                                   MPIL_Comm_gps(3)