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       MPI_Recv - Performs a standard-mode blocking receive.


C Syntax

       #include <mpi.h>
       int MPI_Recv(void *buf, int count, MPI_Datatype datatype,
            int source, int tag, MPI_Comm comm, MPI_Status *status)

Fortran Syntax

       INCLUDE 'mpif.h'
            <type>    BUF(*)

C++ Syntax

       #include <mpi.h>
       void Comm::Recv(void* buf, int count, const Datatype& datatype,
            int source, int tag, Status& status) const

       void Comm::Recv(void* buf, int count, const Datatype& datatype,
            int source, int tag) const


       count     Maximum number of elements to receive (integer).

       datatype  Datatype of each receive buffer entry (handle).

       source    Rank of source (integer).

       tag       Message tag (integer).

       comm      Communicator (handle).


       buf       Initial address of receive buffer (choice).

       status    Status object (status).

       IERROR    Fortran only: Error status (integer).


       This  basic  receive  operation,  MPI_Recv, is blocking: it returns only after the receive
       buffer contains the newly received message. A receive can  complete  before  the  matching
       send has completed (of course, it can complete only after the matching send has started).

       The  blocking  semantics  of this call are described in Section 3.4 of the MPI-1 Standard,
       "Communication Modes."

       The receive buffer contains a number (defined  by  the  value  of  count)  of  consecutive
       elements.  The first element in the set of elements is located at address_buf. The type of
       each of these elements is specified by datatype.

       The length of the received message must be less than or equal to the length of the receive
       buffer. An  MPI_ERR_TRUNCATE is returned upon the overflow condition.

       If  a  message  that  is  shorter than the length of the receive buffer arrives, then only
       those locations corresponding to the (shorter) received message are modified.


       The count argument indicates the maximum number of entries of type datatype  that  can  be
       received  in  a  message.  Once  a  message is received, use the MPI_Get_count function to
       determine the actual number of entries within that message.

       To receive messages of unknown length, use the MPI_Probe function. (For  more  information
       about  MPI_Probe  and MPI_Cancel, see their respective man pages; also, see Section 3.8 of
       the MPI-1 Standard, "Probe and Cancel.")

       A message can be received by a receive operation only if it is addressed to the  receiving
       process, and if its source, tag, and communicator (comm) values match the source, tag, and
       comm values specified by the receive  operation.  The  receive  operation  may  specify  a
       wildcard  value  for  source  and/or  tag,  indicating  that  any  source  and/or  tag are
       acceptable. The wildcard value for source is source = MPI_ANY_SOURCE. The  wildcard  value
       for  tag  is  tag  =  MPI_ANY_TAG. There is no wildcard value for comm. The scope of these
       wildcards is limited to the proceses in the group of the specified communicator.

       The message tag is specified by the tag argument of the receive operation.

       The argument source, if different from MPI_ANY_SOURCE, is specified as a rank  within  the
       process   group  associated  with  that  same  communicator  (remote  process  group,  for
       intercommunicators).  Thus,  the  range  of  valid  values  for  the  source  argument  is
       {0,...,n-1} {MPI_ANY_SOURCE}, where n is the number of processes in this group.

       Note  the  asymmetry  between  send and receive operations: A receive operation may accept
       messages from an arbitrary sender; on the other hand, a  send  operation  must  specify  a
       unique  receiver.  This  matches  a "push" communication mechanism, where data transfer is
       effected by the sender (rather than a "pull" mechanism, where data transfer is effected by
       the receiver).

       Source = destination is allowed, that is, a process can send a message to itself. However,
       it is not recommended for a process to send messages to itself using the blocking send and
       receive  operations  described  above, since this may lead to deadlock. See Section 3.5 of
       the MPI-1 Standard, "Semantics of Point-to-Point Communication."

       If your application does not need to examine the status field, you can save  resources  by
       using  the  predefined  constant  MPI_STATUS_IGNORE  as  a  special  value  for the status


       Almost all MPI routines return an error value; C routines as the value of the function and
       Fortran  routines in the last argument. C++ functions do not return errors. If the default
       error handler is set to MPI::ERRORS_THROW_EXCEPTIONS, then  on  error  the  C++  exception
       mechanism will be used to throw an MPI::Exception object.

       Before  the  error value is returned, the current MPI error handler is called. By default,
       this error handler aborts the MPI job, except for I/O function errors. The  error  handler
       may    be   changed   with   MPI_Comm_set_errhandler;   the   predefined   error   handler
       MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not
       guarantee that an MPI program can continue past an error.