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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"><head>	<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />	<style type="text/css">	body { font-family: Verdana, Arial, Helvetica, sans-serif;}	a.at-term {	font-style: italic; }	</style>	<title>Receiving a Message with Point-to-Point Protocol</title>	<meta name="Generator" content="ATutor">	<meta name="Keywords" content=""></head><body> <p>While there are a variety of methods for sending messages, there is only one for receiving a message from a remote processor. The MPI_RECV function has the following characteristics:</p>

<h3>Standard Receive</h3>

<ul>
<li>
Completion Criteria: Completes when data has been received and can be used in the program</li>

<li>
Has remote completion semantics</li>
</ul>

<p>While only one version of the receive function exists, this function does exist in both blocking and non-blocking form.</p>

<p class="codelang">
C:</p>

<pre><code>int MPI_Recv(void *buf, int count, MPI_Datatype datatype,
int source, int tag, MPI_Comm comm, MPI_Status *status)</code></pre>

<p class="codelang">
Fortran:</p>

<pre><code>CALL MPI_RECV(BUF, COUNT, DATATYPE, SOURCE, TAG, COMM, STATUS, IERROR)

TYPE           BUF(*)
INTEGER    COUNT, DATATYPE, DEST, TAG
INTEGER    COMM, STATUS(MPI_STATUS_SIZE), IERROR</code></pre>

<h3>Example</h3>

<p>Building on the MPI_SEND example, code will be added to have the process with Rank 1 receive the data sent by the process with Rank 0.  To be run with only 2 processes.</p>

<p class="codelang">
Fortran:</p>

<pre><code>      PROGRAM SEND_EXAMPLE
      INCLUDE 'mpif.h'
      PARAMETER ELEMENTS=10
      REAL PRESSURE(ELEMENTS)
      INTEGER SOURCE,DESTINATION,IERROR

      CALL MPI_INIT(IERROR)

      DESTINATION=1
      DO I=1,ELEMENTS
        PRESSURE(I)=I*2.334
      ENDDO

      IF (MYID.EQ.0) THEN
        CALL MPI_SEND(PRESSURE,ELEMENTS,MPI_REAL,DESTINATION,
     & 0,MPI_COMM_WORLD,IERROR)
      ENDIF

      IF (MYID.EQ.1) THEN
        CALL MPI_RECV(NEW_PRESS,ELEMENTS,MPI_REAL,SOURCE,
     & 0,MPI_COMM_WORLD,STATUS,IERROR)
      ENDIF
     
      CALL MPI_FINALIZE(IERROR)
      STOP
      END</code></pre>

<p>For a communication to succeed:</p>

<ul>
<li>
Sender must specify a valid destination rank</li>

<li>
Receiver must specify a valid source rank</li>

<li>
The communicator must be the same</li>

<li>
Tags must match</li>

<li>
Receiver's buffer must be large enough</li>
</ul></body></html>
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