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<TITLE>8.8 Case Study: Earth System Model</TITLE>
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<B> Next:</B> <A NAME=tex2html3198 HREF="node103.html" tppabs="http://www.dit.hcmut.edu.vn/books/system/par_anl/node103.html">8.9 Summary</A>
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<H1><A NAME=SECTION03580000000000000000>8.8 Case Study: Earth System Model</A></H1>
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<P><A NAME=14234>&#160;</A><IMG BORDER=0 ALIGN=BOTTOM ALT="" SRC="img1053.gif" tppabs="http://www.dit.hcmut.edu.vn/books/system/par_anl/img1053.gif">
<BR><STRONG>Figure 8.14:</STRONG> <em> Communicators and intercommunicators in an earth system model.
Available processes are partitioned into three disjoint groups, each
with its own communicator used for internal communication.
Intercommunicators allow the atmosphere model to communicate with the
ocean model and graphics model.</em><A NAME=figmp4>&#160;</A><BR>
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We conclude by showing how the earth system model introduced in
Chapter <A HREF="node14.html#chap2" tppabs="http://www.dit.hcmut.edu.vn/books/system/par_anl/node14.html#chap2">2</A> can be constructed in a modular fashion by using
MPI communicators.  In particular, we consider a hypothetical model
constructed
<A NAME=13413>&#160;</A>
as a parallel composition of atmosphere, ocean, and graphics
<A NAME=13414>&#160;</A>
components.  The atmosphere and ocean models execute concurrently and
exchange data periodically; in addition, the atmosphere model sends
data periodically to the graphics component, which performs data
reduction and rendering functions and outputs high-quality graphics.
We allocate the same number of processes to each component; this
approach is unlikely to be efficient in practice, but simplifies the
presentation.
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<P><A NAME=progmpes>&#160;</A><IMG BORDER=0 ALIGN=BOTTOM ALT="" SRC="img1054.gif" tppabs="http://www.dit.hcmut.edu.vn/books/system/par_anl/img1054.gif"><P>
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Program <A HREF="node102.html#progmpes" tppabs="http://www.dit.hcmut.edu.vn/books/system/par_anl/node102.html#progmpes">8.9</A> implements this modular structure
(Figure <A HREF="node102.html#figmp4" tppabs="http://www.dit.hcmut.edu.vn/books/system/par_anl/node102.html#figmp4">8.14</A>).  The first two lines partition available
processes into the three equal-sized, disjoint process groups that
will be used to execute the three components.  The code following the
``if'' statement establishes intercommunicators that link the
atmosphere model with the ocean and graphics components, and initiates
execution of the three components.  Part of the ocean model code is
shown also.  This performs a reduction within the ocean model
processes by using <tt> MPI_ALLREDUCE</tt> and the intracommunicator <tt>
comm</tt>.  Then, it exchanges data with corresponding processes in the
atmosphere model by using the intercommunicator <tt> atm_ocn</tt>.
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<B> Next:</B> <A NAME=tex2html3198 HREF="node103.html" tppabs="http://www.dit.hcmut.edu.vn/books/system/par_anl/node103.html">8.9 Summary</A>
<B>Up:</B> <A NAME=tex2html3196 HREF="node94.html" tppabs="http://www.dit.hcmut.edu.vn/books/system/par_anl/node94.html">8 Message Passing Interface</A>
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<I>&#169 Copyright 1995 by <A href="msgs0.htm#6" tppabs="http://www.dit.hcmut.edu.vn/books/system/par_anl/tppmsgs/msgs0.htm#6">Ian Foster</a></I>
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