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MPI: Difference between revisions
→Communication
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Note that the <tt>datatype</tt> argument, specifying the type of data contained in the <tt>message</tt> buffer, is a variable. This is intended to provide a layer of compatibility between processes that could be running on architectures for which the native format for these types differs. It is possible to register new data types, but for this tutorial we will only use the predefined types provided by MPI. | Note that the <tt>datatype</tt> argument, specifying the type of data contained in the <tt>message</tt> buffer, is a variable. This is intended to provide a layer of compatibility between processes that could be running on architectures for which the native format for these types differs. It is possible to register new data types, but for this tutorial we will only use the predefined types provided by MPI. There is a predefined MPI type for each atomic data type in the source language (for C: <tt>MPI_CHAR</tt>, <tt>MPI_FLOAT</tt>, <tt>MPI_SHORT</tt>, <tt>MPI_INT</tt>, etc. and for Fortran: <tt>MPI_CHARACTER</tt>, <tt>MPI_INTEGER</tt>, <tt>MPI_REAL</tt>, etc.). You can find a full list of these types in the references provided below. | ||
<tt>MPI_Recv</tt> works in much the same way as <tt>MPI_Send</tt>. Referring to the function prototypes below, <tt>message</tt> is now a pointer to an allocated buffer of sufficient size to store <tt>count</tt> instances of <tt>datatype</tt>, to be received from process <tt>rank</tt>. <tt>MPI_Recv</tt> takes one additional argument, <tt>status</tt>, which should, in C, be a reference to an allocated <tt>MPI_Status</tt> structure, and, in Fortran, be an array of <tt>MPI_STATUS_SIZE</tt> integers. Upon return it will contain some information about the received message. Although we will not make use of it in this tutorial, the argument must be present. | <tt>MPI_Recv</tt> works in much the same way as <tt>MPI_Send</tt>. Referring to the function prototypes below, <tt>message</tt> is now a pointer to an allocated buffer of sufficient size to store <tt>count</tt> instances of <tt>datatype</tt>, to be received from process <tt>rank</tt>. <tt>MPI_Recv</tt> takes one additional argument, <tt>status</tt>, which should, in C, be a reference to an allocated <tt>MPI_Status</tt> structure, and, in Fortran, be an array of <tt>MPI_STATUS_SIZE</tt> integers. Upon return it will contain some information about the received message. Although we will not make use of it in this tutorial, the argument must be present. | ||