),</span> <span class="k">DIMENSION</span><span class="p">(:),</span> <span class="k">ALLOCATABLE</span><span class="p">,</span> <span class="k">INTENT</span><span class="p">(</span><span class="n">INOUT</span><span class="p">)</span>  <span class="kd">::</span> <span class="n">flag</span>
  <span class="c">!! Flag that indicates whether particles are followed in the</span>
  <span class="c">!! simulation (flag=1), or not (flag=0).</span>
  <span class="kt">INTEGER</span>                                    