an><span class="p">))</span><span class="o">/</span><span class="p">(</span><span class="n">Y_R</span><span class="p">(</span><span class="n">cc</span><span class="p">)</span><span class="o">*</span><span class="n">Bmag</span><span class="p">(</span><span class="n">cc</span><span class="p">))</span>
     <span class="n">gradB_Z</span><span class="p">(</span><span class="n">cc</span><span class="p">)</span><span class="o">=</span><span class="p">(</span><span class="n">B_R</span><span class="p">(</span><span