ations.hpp</code>): users are encouraged to mark commutative operations as such, because it gives the implementation additional lattitude to optimize the reduction operation.</p></td>
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<td><p><span class="term"><code class="computeroutput">out_value</code></span></p></td>
<td><p>Will receive the result of the reduction operation, but only for the <code class="computeroutput">root</code> process. Non-root processes may omit if parameter; if they choose to supply the parameter, it will be unchanged.