ain</span> <span class="o">=</span> <span class="n">initial</span>
  <span class="k">call </span><span class="n">domain</span> <span class="p">%</span> <span class="n">setSpectrum</span><span class="p">(</span><span class="n">backward_euler</span><span class="p">(</span><span class="n">initial</span> <span class="p">%</span> <span class="n">getSpectrum</span><span class="p">(),&amp;</span>
    <span class="n">tendency</span> <span class="p">%</span> <span class="n">getSpectrum</span><span class="p">(),</spa