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    <p>It's true that OpenMP reduction can't handle such overloaded operators. However, there is an alternative. One way to rewrite a reduction in OpenMP is to use the <code>nowait</code> and <code>atomic</code> paramters. <a href="http://bisqwit.iki.fi/story/howto/openmp/#ReductionClause" rel="nofollow noreferrer">http://bisqwit.iki.fi/story/howto/openmp/#ReductionClause</a> .This is just as fast as the normal way. </p> <p>If you replace <code>atomic</code> with <code>critical</code> you can use more complex overloaded operators. This is not as fast as using <code>atomic</code> but it's still works well in my experience.</p> <p>I did this so I could use operators that operate on 4 or 8 floats at once (with SEE or AVX). <a href="https://stackoverflow.com/questions/15430069/reduction-with-openmp-with-sse-avx">reduction with OpenMP with SSE/AVX</a></p> <p>Edit: I changed your code to reflect what I think would do what you want.</p> <pre><code>void CEnergymulti::forcetwobody(vector&lt;CMolecule*&gt; m_mols,CPnt force0,CPnt torque0) { const int nmol=m_mols.size(); force0.zero(); torque0.zero(); #pragma omp parallel { CPnt force0_private; CPnt torque0_private; force0_private.clear(); torque0_private.clear(); #pragma omp for nowait for(int j=1;j&lt;nmol;j++) { CPnt forcetemp,torquetemp; forcetemp.zero(); torquetemp.zero(); vector&lt;CMolecule*&gt; twomols(2); twomols.clear(); twomols.push_back(m_mols[0]); twomols.push_back(m_mols[j]); CMolecule::polarize_mutual(twomols,false, 1000); twomols[0]-&gt;computeMol_Force_and_Torque(forcetemp,torquetemp); force0_private+=forcetemp; torque0_private+=torquetemp; } #pragma omp critical { force0 += force0_private; torque0 += torque0_private; } } REAL converter=COUL_K*IKbT; force0*=converter; torque0*=converter; return; } </code></pre>
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    1. COI think the second pragma (i.e. `#pragma omp parallel for nowait`) should be `#pragma omp for nowait`, i.e. without the parallel (The parallel construct has already been setup outside it). My compiler complains that you cannot have a nowait alongside a parallel for, as there is supposed to be an implicit barrier after the parallel for. Seems like nowait and parallel for are conflicting directives.
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