an class="p">(</span><span class="mi">1</span> <span class="o">+</span> <span class="n">erf</span><span class="p">(</span><span class="n">pos</span><span class="o">/</span><span class="p">(</span><span class="n">std</span><span class="o">*</span><span class="n">np</span><span class="o">.</span><span class="n">sqrt</span><span class="p">(</span><span class="mi">2</span><span class="p">))))</span>
        <span class="n">f</span> <span class="o">=</span> <span class="n">np</span><span class="o">.</span><span 