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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
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<a name="mpi.design"></a><a class="link" href="design.html" title="Design Philosophy">Design Philosophy</a>
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</h2></div></div></div>
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<p>
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The design philosophy of the Parallel MPI library is very simple: be both convenient
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and efficient. MPI is a library built for high-performance applications, but
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it's FORTRAN-centric, performance-minded design makes it rather inflexible
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from the C++ point of view: passing a string from one process to another is
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inconvenient, requiring several messages and explicit buffering; passing a
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container of strings from one process to another requires an extra level of
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manual bookkeeping; and passing a map from strings to containers of strings
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is positively infuriating. The Parallel MPI library allows all of these data
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types to be passed using the same simple <code class="computeroutput"><span class="identifier">send</span><span class="special">()</span></code> and <code class="computeroutput"><span class="identifier">recv</span><span class="special">()</span></code> primitives. Likewise, collective operations
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such as <code class="computeroutput"><a class="link" href="../boost/mpi/reduce.html" title="Function reduce">reduce()</a></code> allow arbitrary data types
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and function objects, much like the C++ Standard Library would.
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</p>
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<p>
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The higher-level abstractions provided for convenience must not have an impact
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on the performance of the application. For instance, sending an integer via
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<code class="computeroutput"><span class="identifier">send</span></code> must be as efficient as
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a call to <code class="computeroutput"><span class="identifier">MPI_Send</span></code>, which means
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that it must be implemented by a simple call to <code class="computeroutput"><span class="identifier">MPI_Send</span></code>;
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likewise, an integer <code class="computeroutput"><a class="link" href="../boost/mpi/reduce.html" title="Function reduce">reduce()</a></code> using <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">plus</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span></code> must
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be implemented with a call to <code class="computeroutput"><span class="identifier">MPI_Reduce</span></code>
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on integers using the <code class="computeroutput"><span class="identifier">MPI_SUM</span></code>
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operation: anything less will impact performance. In essence, this is the "don't
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pay for what you don't use" principle: if the user is not transmitting
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strings, s/he should not pay the overhead associated with strings.
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</p>
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<p>
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Sometimes, achieving maximal performance means foregoing convenient abstractions
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and implementing certain functionality using lower-level primitives. For this
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reason, it is always possible to extract enough information from the abstractions
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in Boost.MPI to minimize the amount of effort required to interface between
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Boost.MPI and the C MPI library.
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<td align="right"><div class="copyright-footer">Copyright © 2005-2007 Douglas Gregor,
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Matthias Troyer, Trustees of Indiana University<p>
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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file LICENSE_1_0.txt or copy at <ulink url="http://www.boost.org/LICENSE_1_0.txt">
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http://www.boost.org/LICENSE_1_0.txt </ulink>)
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