class="n">vstack</span><span class="p">([</span><span class="n">n_air</span><span class="p">,</span> <span class="n">n_Ag</span><span class="p">,</span> <span class="n">n_air</span><span class="p">])</span><span class="o">.</span><span class="n">T</span>  <span class="c1"># Transpose to match expected shape (Nlayers x Nfreq)</span>
<span class="n">d_stack</span> <span class="o">=</span> <span class="n">np</span><span class="o">.</span><span class="n">vstack</span><span class="p">([</span><span class="n">d_a