s){};</div><div class="line"><a name="l00052"></a><span class="lineno">   52</span>&#160;        <span class="keywordtype">size_t</span> operator()(<span class="keywordtype">size_t</span> particle_entry)<span class="keyword"> const </span>{ <span class="keywordflow">return</span> body_part_particles_[particle_entry]; };</div><div class="line"><a name="l00053"></a><span class="lineno">   53</span>&#160;    };</div><div class="line"><a name="l00054"></a><span class="lineno">   54</span>&#160;</div><div class=