 available options</span>
<span class="sd">        Return:</span>
<span class="sd">        Nothing if the user provides an appropriate fitting model</span>
<span class="sd">        Else it will throw an error</span>

<span class="sd">        &quot;&quot;&quot;</span>
        <span class="k">if</span> <span class="bp">self</span><span class="o">.</span><span class="n">fit_function</span> <span class="ow">in</span> <span class="bp">self</span><span class="o">.</span><span class="n">available_functions</span><